For starters, a "sewer" can refer to one of two things. First is a storm drain, a system for carrying rainwater and snowmelt off the streets and into a nearby body of water. Second is a sanitary sewer, where the pipes from homes and buildings empty their wastewater, leading to sewage treatment facilities. There are places where the two overlap, but when this article refers to sewers, it is most likely referring to the latter.
In real life, most modern sanitary sewers consist of pipes too small for an adult to enter. They typically range from a few inches in width coming from individual properties, to about 2-3 feet wide in the street. Even these largest ones can at best only be crawled through, and then only if they are currently empty.
Older sewer systems may consist of underground canals with narrow walkways on the side. These canal systems are the basis of this trope, but very few creatures, humans especially, would actually be able to survive in sewers for any extended length of time. It's pitch black (sewer workers bring their own lighting), chilly even in the summer (50-60 degrees year-round), and there's little oxygen and a plethora of noxious gases from sewage, making the air highly unsuitable for breathing without specialized equipment.
Sewers featured in video games and any other form of fiction, however, are usually absurdly spacious underground rivers with ample room to move, enabling characters to avoid stepping into the actual sewage (often a good thing, since in many games, contact with sewer water is inherently harmful). These underground passages have more in common with the catacombs of Paris than any actual sewer system. The dim lighting, labyrinthine passages, and resident rats and alligators provide the perfectly suitable setting for heroes to chase criminals and/or monsters through. Occasionally, the place is so big people elect it as their home. It's not unusual to find whole shanty towns built in ludicrously large sewer or ex-sewer canals, coming close to transforming into an Underground City. And somehow there's always adequate lighting, warmth, and breathable air. Presumably, there's no bodily waste down there because Nobody Poops.
Such sewers also tend to be connected to a multitude of locations throughout the city, accessed through manholes with easily removable lids (in real life, manhole covers are heavy and lack obvious handles to prevent this exact thing), granting access directly into otherwise secure buildings: a perfect way for suspicious types to travel without detection, noxious fumes notwithstanding.
In fantasy or historical fiction, this trope becomes anachronistic. Until the Industrial Revolution, the preferred method of waste removal was pouring it into ditches in the street where the rain would wash it away (sooner or later). However, this could be justified by fantasy societies (such as dwarves) that are more industrialized than their medieval human counterparts.
This trope may coincide with the much narrower Sinister Subway, and both are generally connected to the all-encompassing Dungeon Town. For an alternate route, see the Air-Vent Passageway. These are all standard issue for The Alcatraz. And don't forget the Abandoned Maintenance Tunnels.
Real life spacious sewers do exist. See IAMA Drainer. In practice, the "underground tunnel network where homeless people and thieves live" of urban lore does exist in a few industrialized cities. They are usually a system of technical tunnels built to accommodate water from various sources, electrical cables, storage spaces for the underground rail systems, and so on. The reason for its spacious construction being the fact it has to allow maintenance workers and sometimes their vehicles to run inside.
Compare Unnecessarily Large Interior and Underground City.
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Anime & Manga
Digimon Adventure managed to fit this trope. Despite, you know, a lack of any reason for sewers to exist in the digital world. But then, that's the digital world for you. Considering that the digital world includes such gems of architecture as an upside-down, physics-defying pyramid, an improbably large sewer is the least of their engineering problems.
One episode of Excel♥Saga had everybody traveling in a large sewer underneath F City, all the while being stalked by Puchuus.
Which is based on a chapter in the original manga, minus the Puchuus. It makes sense that the sewers would be large, since they have to accommodate ACROSS's headquarters.
Heat Guy J featured an underground sewer city that leached off of the technologically advanced city above. It was freer, pleasant and considerably more crowded than other examples listed in this trope. (Which is strange, as one would think illness and death would be rampant in a crowded, airless city situated next to a river of raw sewage.)
In Bleach, the only reason Ichigo survived so long was because he was able to move around in Seireitei's ungodly huge sewer system. Although they were also supply routes, which makes a bit more sense. The non-Shinigami members of Soul Society do not need to eat. Which, while not quite at Nobody Poops level, it's more like 5% percent poops. (If even that - everything in Soul Society is just spirit energy, so it's uncertain whether eating results in any waste products.)
Episode 31 of Sailor Moon has a chase lead into one of these. At least the smell gets remarked upon.
While a cat did it get stuck in there, it was really big, due to being a crystal carrier.
Once Luna has pushed the large cat into the pipe, Zoicite has no problems following them, which is lampshaded in the abridged series:
Zoicite: I defy physics!
Used plausibly in Berserk, as they're under a rather large castle/fortified town in around the time large sewer tunnels would have been built. Also avoids the "hero doesn't actually have to walk in the sewage" thing, because it's weird to imagine someone fighting for their lives while caked with poop from the knees down. Realistic, though.
The sewer system under Mahora in Mahou Sensei Negima! is huge. Huge enough for people to have battles against groups of Mechamooks and Spider Tanks. There's even a massive, cavernous room there that contained an invading army of those plus a few Humongous Mecha.
Ashford Academy's water distribution tunnels in Code Geass are ridiculously huge, considering it only services the school.
Behemoth, a massive team in Air Gear, has its HQ in a massive sewer that can hold more than 1000 riders and a massive construction excavator. Possibly justified in that it was a sort of sewage plant, not just a sewer, and it was renovated.
In Fullmetal Alchemist, Ran Fan escapes through the sewers of Central after she and Ling fight Wrath. Scar is also shown traversing sewers on multiple occasion. However, this may be justified as the city, including sewer networks, has been created entirely under the rule of Father, and the sewers connect to his underground base.
The sewer network under the imperial capital in Pumpkin Scissors is big enough that it contains as many people as the city above. Also, you can drive and drift in it.
Spice and Wolf features a sewer system big enough to fit a massive wolf in, with enough room left over for said wolf to fight a group of soldiers. This is somewhat justified as they were originally built the the church to use as escape routes.
Pokémon episode "Leading A Stray!" (The Stray Hoeruko!)". Ash and friends travel through a sewer large enough for a Wailmer to swim in.
The firing range that the main characters of Noir use for target practice is a bulls-eye chalked onto the wall of a sewer tunnel. Given that nobody in the series mentions that they smell funny, they must have found a highly effective brand of soap.
In one episode of Kimba the White Lion, Kimba accidentally gets himself lost in the sewer system in Paris and then has to fight an elderly leopard that has been thought as a monster living in the sewers.
In Wolfs Rain Kiba and Hige spend an ENTIRE night sleeping in one in Episode 3 and neither of them ends up falling sick or anything like that. Later in the same episode the two of them along with Toboe trudge through the sewers with no problem at all with Hige complaining he "doesn't like smelly places" at the most.
In Magic: The Gathering, the sewers of the city-world of Ravnica are so spacious that they count as cities unto themselves; justified in that they are old cities that have been built over. They're mostly used by the Golgari elves and humans to dispose of waste and grow produce for the surface-dwellers, and by Dimir and Rakdos criminals as safe havens, though they also have their fair job of wandering monsters. The place is even referred to as The Undercity.
In the later expansion Shards of Alara, the plane of Esper has a sewer system known as the Tidehollow, where the plane's more unsavory elements salvage Etherium scrap. Predictably, most of the shard's black mana comes from this region.
As mentioned above, the New York (and London, and Chicago) sewers are home to the Morlocks in X-Men.
The original Morlock Tunnels in New York were not sewers or storm drains at all, but a long-abandoned Army construction project originally intended to serve as a mass fallout shelter and then abandoned partway through construction due to cancellation of funding.
Played straight in the X-Men Legends RPG, in which the Morlock Tunnels are a sewer system, though it seems to be a storm sewer rather than a sanitary sewer.
There's also a subfaction of Morlocks who tunnel through the earth nomadically, presenting the flipside to the drain dwellers' coin.
During a period in Superman comics when Applied Phlebotinum had reinvented Metropolis as a 64th century ultra-city, the sewers were a vast network of extremely clean looking waterways, patrolled by genetically engineered creatures who consumed the city's waste and tasted like chicken. Also, a homeless guy who'd found a rubber dinghy and an outboard motor on a pole and reinvented himself as the mythic archetype of the Ferryman.
Regular old Metropolis has the Underworld, home to ... humanoid-but-not-human creatures, and a few humans who can't find anyplace better to live. The Underworld is mostly either natural caverns or excavated by the Underworlders themselves, but it does connect with Metropolis' underground public works (subways, technical tunnels, storm drains, etc.).
In the Batman comics, Gotham City has a spacious and labyrinthine sewer system that often serves as a base of operation to villains such as Killer Croc and the Rat-Catcher.
Its sequel Dark Victory has Two-Face, Joker, Scarecrow, Mr. Freeze, Poison Ivy...yeah, the sewers are large enough to be a small town.
This is sometimes blamed on a lack of proper planning permission system.
Said sewers are also connected to the Batcave (and one issue of Batman/Superman shows that this entrance is guarded by Alfred with a shotgun, leaving Superman to remark "You didn't have a spare Mr. Freeze gun you could've loaned him?"). Those sewer accesses are ALWAYS big enough to accommodate the Batmobile, Batsub and the Batboat moving at outright irresponsible speeds.
In fact in Dark Victory, Two-Face and his gang actually stumble into the Batcave by accident, after fleeing through the sewers from their compromised base.
In the "What If?" type story, The Punisher Kills The Marvel Universe, the Punisher's first victims are Spider-Man and Venom, who are fighting in a sewer. Spider-Man is actually able to jump around (Meaning he flies over Venom's head by a good five feet) in the sewer.
In issue #23 of the original Wolverine ongoing series, Wolverine has trapped General Coy and Prince Baran in the Madripoor sewers. There is apparently enough room for all three to run around without crouching or bumping into things, and Wolverine is able to leap at his two enemies to scare them into running.
Every single incarnation of the Teenage Mutant Ninja Turtles, where they have 2-5 bedrooms, a living room, kitchen, a training area, AND a garage for the Turtle Van (let's not think about the blimp for now...). It's unclear if Splinter's meditation room and Don's workshop are part of their bedrooms or separate, but the latter's easy to picture considering how huge their underground palace already is. Although the sewers in almost every section of the TMNT franchise resemble the real-life New York storm drain system more than any sewer, and it wouldn't be the first time people have gotten the two terms confused.
Some incarnations (like movies past the first) place the Turtles' palace in an abandoned subway station, with the Van being stored in nearby abandoned warehouses. However, those locations are always connected to the sewer system, and said sewers are inevitably big enough for the Turtles (especially Michelangelo) to be able to skate and do half-pipes in the sewer pipes.
In the Hellboy spin-off Lobster Johnson: The Iron Prometheus, the Lobster is able to travel by boat through the New York sewer system. And it's mentioned that there is a subterranean cannibal tribe, though not a bad as the ones under London and Paris.
The Eel would make his lair in one of these (seriously, the ceiling has got to be like fifteen feet high) in early Marvel Comics, laying low after his defeat by the Human Torch in his first appearance.
Yeagar: The sewer system is big enough for you guys to crawl through it? Artax:Crawl through? are you kidding? The sewer caverns are huge! You'd almost think the town had been trying to cause the bar's foundation to cave in and wash everything out to sea. Barman: Gee, with my upstanding clientele? Go figure.
The sewers of Sin City are apparently pretty large. Marv is able to swim through them via the harbor and make it to anothe rpart of town in The Long Goodbye. Dwight, meanwhile, takes on an IRA mercenary in the sewers in The Big Fat Kill.
In The Beano the Ratz appear to live in a sewer large enough for a number of things and the sewer enables them to easily get into the houses of humans. However the sewers have never been shown to be large enough to fit humans down them.
Kraken was a comic serialized in the 1980's Spanish magazine Metropol, and set in the fictional city of the same name. The Metropol Sewer Police had patrol boats to move around, and the sewers themselves were connected to a whole not-quite-abandoned subterranean city, complete with disused factories and all (a reference to the classic Fritz Lang film) Among the inhabitants of this massive underworld were homeless vagabonds, criminal gangs, long-forgotten veterans of an old civil war and the eponymous Kraken itself, an amorphous, all-devouring tentacled behemoth that kept getting bigger and occupying larger portions of the system in spite of all the efforts to contain it.
Mortadelo y Filemón: Many times, a mission will require that Mortadelo and Filemón go down to the sewers, which are big enough to fit Mortadelo quite well (Word of God is that Mortadelo is 1'80 metres tall).
In Mass Foundations, the trio of protagonists sneak into the abandoned mining facility to capture Shepard’s body through the wastewater pipe. Downplayed, as mining always produces large quantities of wastewater and the pipes of the size shown (they’re implied to be just large enough to move through) are quite likely to be used. Because the facility processes eezo, the water is radioactive as well; they could only get through because of The Courier's Rad-X.
Films — Animation
In Flushed Away we see the sewers only from the rats' perspective, but for their purposes, at least, the sewer is large enough for a sprawling city.
Shrek the Third. This is justified because it was a secret escape route connected to the palace in case of attack.
Shua flees the Ecoban law enforcement at the start of Sky Blue. His path takes him through both an Absurdly Spacious Sewer system and the the Air Vent system.
The secret hideout of the cat gang in An American Tail. Justified for being in New York City in 1885 (they were that big back then) and that from the viewpoints of cats and mice everything is bigger.
The Gypsies in Disney's The Hunchbackof Notre Dame all live inside a giant sewer system located underneath the streets of medieval Paris. Unfortunately, Frollo actually knows where that location is... Justified because said sewers system actually exists
Hellboy: Blood and Iron starts with Hellboy fighting a giant mystic bull robot in a sewer system rivaling a cathedral in size.
Hellboy: It's like a maze down here. A maze of crap.
Films — Live-Action
In Aliens vs. Predator: Requiem, the town of Gunnison's sewer system is big enough for two grown men to walk through easily, has ducts big enough for chestbursters to hide in, is easy to access by both humans and xenomorphs, and is the setting of a major fight scene between a Predator and two xenomorphs.
"Is that a couch?...Its better than ours!"
In Blade II, the sewers underneath the city are HUGE. So big, in fact, that scores of Reavers can stand wall to wall.
In The Third Man, the spacious sewers of Vienna play a vital role. The ending of the film was largely shot in the city's real sewers, and features the villain being chased by a Real Life squad of policemen that existed for the sole purpose of patrolling its sewers!
Sweeney Todd: The Demon Barber of Fleet Street: Sweeney Todd and Mrs. Lovett search for their assistant Toby in one of these, which is also featured in the title sequence. While this sewer system is large enough for them to walk upright in, it's also described as being the source of the unusually foul smells of Mrs. Lovett's bakery.
In the original Sweeney Todd story, "The String of Pearls", the tunnels below Fleet Street were how Sweeney got the bodies of his victims to Mrs. Lovett for baking into pies, since her pie shop was right across the street from his barbershop. Previously, he'd had a good number of dead dudes down there, since he dispatched his victims by using a trick barber's chair to dump them into his basement, taking his razor to any who survived the fall. And unlike the musical, this eventually got the two of them caught when the Bow Street Runners investigated.
According to the Korean monster film The Host, most of the sewers in Seoul are big enough for torchlight not to be seen on the roof — or, for that matter, for a BIG FREAKING TADPOLE MONSTER to charge through them.
The pipe systems in The Matrix series are described as sewers which are big enough for whole hovercrafts to comfortably navigate through them, and a city inhabited by thousands of people in its lower depths. The sewers were the only remains of the human cities destroyed in the war with the machines. That's just in "The Desert Of The Real". The Matrix itself has a sewer system beneath the Mega-City that rivals the Mines of Moria — chambers hundreds of feet wide and deep connected by twisty catacomb-like tunnels.
If you thought Alien was the first movie to have creepy monsters being stalked through dark tunnels with flamethrowers, you're wrong. The classic B&W 1954 sci-fi movie Them! climaxes with a hunt through the Los Angeles storm sewer system (including jeeps with mounted machine-guns) for the giant radioactive ants.
This film is parodied in a sidequest in Fallout 3 called Those!, where the player has to kill radioactive, fire-breathing ants in a similarly abandoned sewer system (which the game is rife with.)
Actually, the underground structures you explore are Metro tunnels, which would kind of explain all of the broken down subway cars.
This is justified, as several Real Life documentaries state that the catacombs in Venice have access through manhole covers to pipes running through them at points form the sewer system...
The catacombs in Istanbul in From Russia with Love. While big enough for James Bond and his current girl to navigate through, they are extremely cramped as well.
Dutch Film Amsterdamned had the hero police investigator investigate (that's what Police investigators do... investigate...) the source of the bad guy maniac killer's hidden hidey hole... which was a gigantic piece of sidewalk with a pseudo-canal right next to it, obviously filmed on a filmset cause Amsterdam doesn't even have sewers like that, unlike Paris. It was filmed in Utrecht, a different city with canals.
Averted in the 1990s Teenage Mutant Ninja Turtles films; the Turtles are clearly walking through storm drains, not sanitary sewers. Their home base is an abandoned control station, so while there are a couple rooms, they're small rooms. Their gigantic lair in the second movie is a deserted "subway" station (Actually it looks more like a Pneumatic Transit station with a subway car parked inside), not a sewer at all.
In Demolition Man, the "Wasteland" is the underground sewer system that is home to San Angeles' undesirables. Justified as most of Wasteland is the ruins of Los Angles after a great earthquake.
In Ladyhawke, Phillipe Gaston (a.k.a. "the Mouse") escapes from a dungeon via its sewer. Played straight in that the sewer is only just big enough for a child, and the guard who finds him gone expresses disbelief. However, a real medieval dungeon would not have a sewer of any size at all.
The catacombs in Metropolis approach this, especially with the scene in the massive cathedral-esque underground chamber where Maria holds her religious meetings. Which warrants the question: how did Joh Fredersen completely miss this system of catacombs while building the city, large parts of which — such as the machine rooms, subway, and worker's quarters — are underground?
Cthulhu. A scene beneath the fictional town of Rivermouth was filmed in the real-life Seattle Catacombs, where one of the producers used to work as a tour guide.
S.W.A.T. has a ridiculously roomy sewer in the last chase scene.
In Plunkett And Macleane the title characters use large sewer tunnels to escape the law on several occassions.
One of the locations of the floating crap game in Guys and Dolls, and remarkably clean, too.
Seen in the film The Fugitive. Might be justified as this is out in the country rather than the city.
Penguin's hideout in the zoo is conveniently connected to Gotham City's large sewer system in Batman Returns.
The movie Creep is a horror movie that starts in The London Underground, and the resident monster was living in a secret Abandoned Hospital but there is your fair share of spacious sewers including one section where he keeps humans in large submerged cages with a catwalk above them.
A lot of it was filmed in real, albeit decommissioned, sections of The London Underground, standing in for various bits of underground weirdness. Some sections of the network have been disused for the better part of a century now, and are beginning to look as run down and grotty as a viewer would expect the sewers to look.
Averted in the film El Norte. Two siblings from Guatemala want to get to the US. They're in Mexico, and the only safest, fastest route was through an old sewer pipe. Not only is it small and smelly and they have to crawl on their hands and knees most of the way, but it's full of rats. Disease-ridden rats.
Bane's hideout in The Dark Knight Rises is in the sewers of Gotham. They are large enough to have action scenes in. Justified by the fact he's been using Dagget's construction company to make it so. Also the hideout seems to be the storm drain system and not sanitary sewers.
In the third Rush Hour film, when the guys are taken prisoner. Again, this is justified by the fact that the film is set in Paris, whose sewers really are like that.
Averted in Snow White & the Huntsman when Snow White sends the dwarfs to open the gates prior to her attack by sneaking in through the sewers. This is Played for Laughs when two dwarfs are side by side in the tunnel.
In the 1988 version of The Blob, it's wide enough for a bike to go through. The sewers being so absurdly spacious is actually explained in an easy-to-miss bit of dialogue. The "sewers" are actually an aqueduct system built to prevent flooding from the mountains.
The Lone Wolf gamebook series contains a few Absurdly Spacious Sewers, most notably the Baga-darooz in Barrakeesh, capital of Vassagonia. This sewer is vast enough to house giant lizards and other nasty monsters, and criminals can be condemned to be locked within. Unlike some other fantasy examples, however, it is described as extremely filthy, smelly and insalubrious — just getting an open wound in contact with the water can give you a horrible disease. (As in, Race Against the Clock to get the next Plot Coupon before you have to hack off the infected arm and/or die screaming.)
Disgustingly averted in The Granite Shield when two children infiltrate a castle by climbing up the privy shaft.
Clare Clark's historical novel The Great Stink is all about building an improved London sewer system.
And 160 years later the protagonists in Ben Aaronovitch's Whispers Under Ground not only get to see it in all its fading glory but conduct the occasional gunfight and, strangely, practise for a winter Olympic event.
In Stephen King's IT, crucial events (in both time periods) occur in the sewers under Derry, which feature pipes big enough for adults to walk in without having to bend down, and chambers large enough for multiple adults to have plenty of elbow room.
They call them sewers, but if I'm not mistaken, they were really storm drains, which are big enough to walk through.
Call them whatever you like, they're also apparently big enough to have a friendly gang bang in.
By contrast, there's Stephen King's Rita Hayworth and Shawshank Redemption, later filmed as The Shawshank Redemption. Andy Dufresne does get out via a sewer ... but it's a much smaller one than those in It.
In Garth Nix's Shade's Children, which takes place After the End, the sewer system is the primary path of transportation for La Résistance. Averted very slightly by the fact that the difficulties of walking in a curved pipe and the danger of sudden floods are addressed.
In Eric Nylund's A Game of Universe, some action happens in a sewer, but since there are no walkways they have to do a lot of wading/swimming.
In the Discworld novel Men at Arms, the characters venture into the capacious sewers of Ankh-Morpork. As in the Futurama example below, this is partly justified because some segments of the sewers are older incarnations of the city itself, now buried and paved over. In fact the sewer system itself was paved over, with the modern day residents oblivious to the fact that it ever existed.
Detritus: In Ankh-Morpork even the shit have a street to itself. Truly, this a land of opportunity.
The entirety of Ankh-Morpork is built on the slowly sinking ruins of its past, making it extremely easy for the native/non-native dwarves to tunnel under the city. Morpork doesn't build out from urban sprawl, it builds UP, and then sinks farther and farther.
In The Truth, Sacharissa Cripslock explains the phenomenon to some dwarfs while availing themselves of the exact same eccentricity of architecture. Ankh-Morpork is (somewhere down there) built on soft loam. Gradually, slowly, not so you'd notice until you tripped on the sidewalk, the sturdy foundations of the city sank ever deeper into the ground. At certain points in the city's history, street level was a full story above the entrances of the buildings — ladders and tunnels were used to get across the street. The Author's Note at the beginning explains that this is based on Seattle, below.
Ankh-Morpork has smaller sewers in some sections also, but that doesn't necessarily keep out the Watch, or at least the Buggy Swires/Wee Mad Arthur portion of it. Those two Watchmen are only six inches high, so even a modest sewer is quite spacious by their standards.
The reveal of Harry Potter and the Chamber of Secrets is that the monster of the Chamber is a giant snake that gets around the school using the plumbing. Justified because the Chamber's creator was one of Founders of Hogwarts, who may have planned its inclusion even before his falling-out with the others.
Neal Shusterman's young adult novel Downsiders is about a secret community of people who live underneath New York City and are forbidden to go "topside."
In the early Neal Stephenson book The Big U, devoted role-playing gamers would enter the sewers to game, with the help of a mainframe computer and a form of Mission Control acting as DM. (See the Mazes & Monsters entry below.)
In The War Between the Pitiful Teachers and the Splendid Kids, a spacious sewer inhabited by the Bookworms (smart kids and teacher's pets) is the last refuge of the Kid Hero.
The most realistic examples would include the book 'Felidae on the Road', where protagonist Francis encounters a tribe that lives in the sewers. Justified in that they are cats (and dogs) and so are small enough, they are described as being filthy and the smell down there being noxious, they eat sewer rats, and they have gone blind from the constant darkness of the sewers.
In Les Misérables, when Valjean and Marius escape through the sewers of Paris. However, as shown by the Real Life entry below — and a very lengthy passage in the book itself — the Paris sewers are really like that.
This is mentioned in World War Z. Apparently it made cleaning up the zombies a real bitch.
Montmorency revolved around an escaped criminal robbing some of London's richest citizens, then escaping through the sewers. The spacious nature of London's sewers has been referenced repeatedly above.
In the Deathstalker series, the city of Golgotha has an enormous sewer system for the Empire's homeworld. The Rebellion has a foothold there.
Both Lampshaded and subverted in Sandy Mitchell's Ciaphas Cainnote HERO OF THE IMPERIUM!!! novel Death or Glory. When Cain is trapped in a building surrounded by Orks, he remarks that having sewers and storm drains as a convenient escape route whenever he's trapped is not nearly as common as he would have liked. Played straight in For the Emperor when Cain and Vail go into the city sewers to hunt Tyranids.
And then played somewhat straight in The Emperor's Finest, in which the tunnels under the city are big enough to hold the nearly two meter tall Cain, but not big enough to fit Space Marines.
The Edge Chronicles has a sewer so large that buildings have been constructed inside it.
Conan the Rogue has a sewer system under a corrupt town deliberately altered by thieves to act as transport routes, including hidden entrances and marked locations. Even then, only the main trunk lines are large enough to travel.
One of the Three Investigators books had the young heroes escape the villains in the storm drain system of a very old city. They meet up with some allies rowing a boat through the drain.
In The Saga of Darren Shan absurdly large sewers feature largely in a number of the books most notably an arena of sorts is built in one part of the sewer and the sewers are used as a base of sorts for the mad vampaneze Murlough.
In the book Reliquary, the sequel to The Relic, much of the action takes place in massive underground sewers, storm drains, maintenance tunnels, abandoned pneumatic train systems (!) beneath New York City. Justified as Truth in Television: New York City is said to stand on seven storeys of underground tunnels, and the authors add a postscript backing the veracity of much of their claims about the extensive tunnelwork below the city.
In the second Provost's Dog book, the climactic battle takes place in the sewage system. Though the tides causing the waters to rise is addressed, so that the final battle is actually in the dirty water.
An Absurdly Spacious Rubbish Chute serves as the escape path for Jenna and the Heaps in Magyk.
In The Magician, the second book of The Secrets of the Immortal Nicholas Flamel series, Machiavelli and Dee take Josh into the spacious sewers and then the catacombs in Paris to be Awakened by Mars Ultor. This is justified because Paris does have an incredibly large sewer system that connects to the catacombs. There is even a special branch of the police force that patrols the sewers.
In the Star Trek Novel Verse, the sewers of Ki Baratan (the capital city of Romulus), are apparently rather spacious. Ambassador Spock and the Romulan underground frequently meet down there; in the first ''Titan'' novel, Tuvok goes down to find them. It's basically a city underneath a city.
Pushing Daisies has the most cheerful and attractive looking sewers I've ever seen. At least one character lives in them.
There are Cybermen lurking in London's sewers in two Doctor Who stories ("The Invasion" and "Attack of the Cybermen").
Daleks and their pig slaves lurked in Manhattan's sewers in the two-parter "Daleks in Manhattan"/"Evolution of the Daleks".
New Who also had Cybermen in the "cooling tunnels" beneath Lumic's factory in "Age of Steel", in a Continuity Nod to the previous Cyber-stories.
"The Talons of Weng-Chiang" has highly-unconvincing giant rats guarding the sewer entrance to the villain's lair.
The true size of some sewers can be seen in an episode of Dirty Jobs. The sewer the host explored was so small and cramped that nobody could actually stand up straight, and had to spend all of their time inside bent over.
If you believe Buffy the Vampire Slayer and Angel, sewers in both Sunnydale and Los Angeles are so big that vampires can travel all over the town during the day. There's fourteen million square miles of them, and that's not including a lot of natural cave formations and a gateway to Hell. In "Enemies" it's revealed that the Mayor built Sunnydale "for demons to feed upon", so it makes sense that the sewer system is constructed so as to give easy access to the whole town.
Lampshaded on Angel in "Fredless" when Fred states: "I could build a condo in these sewers."
After watching the entirety of Buffy and Angel, one wonders how those two don't constantly get remarks about their iffy sewage smell. Angel in particular practically lives down there.
One episode of Eureka plays with this, though that wasn't so much a sewer as a sewer and the environmental and recycling center of a town of super geniuses.
On Reaper, Sam, Ben and Sock once had to search the sewers for an escaped soul made of green nuclear-waste goo. The sewers were fairly dank and smelly, but they were easily big enough for three people to walk through.
In the Supernatural episode "Skin", Sam and Dean pursue their quarry into a sewer large enough for them to stand upright, occasionally walk abreast, and a spacious lair for the shapeshifter. Large rusty pipes and large amounts of moisture complete the expected look of an ancient underground despite the episode being set in St. Louis, MO.
Averted in the later episode "No Exit" in which the sewers are extremely small and dark with the Winchesters barely able to make it through
An episode of Popular Mechanics for Kids is devoted to this, when they go into a sewer to look for a ping-pong ball. Being a show about science and facts, they remark that you always need the proper equipment and that it can be dangerous to go into a sewer. It was actually pretty spacious in there; almost hallway like, IIRC.
In Beauty and the Beast, a secret society exists deep underneath New York, in relatively fancy trappings.
Due South episode "Manhunt", the Chicago sewers are not only large enough for three grown men and a wolf, they are large enough for three grown men and a wolf to paddle a canoe through.
Used and averted in The X-Files season 2, episode 2 "The Host." Mulder visits an absurdly spacious sewer in Newark, N.J., and later remarks about its size to a Newark sanitation engineer, who confirms that section as being part of the older system, while the newer parts are not more than 24 inches in diameter.
Played straight in "Teso Dos Bichos".
Played straight with size, but averted with toxicity in an episode of Casualty. It involves two guys who want to win a bet which involved walking to the pub by using the sewers as a shortcut. The guys have oxygen supply, but then they start to run out... That's when the paramedics are called.
Paranoia once had an section simply named "Sewerworld!" in the Send in the Clones adventure. The author observes something to the effect that sewers are remarkably consistent over time. "You could drop a Roman sewer-slave into modern Tokyo's ultra-sanitary system... sure it'd be cruel. But he wouldn't wonder where he was..."
Any sewer in Dungeons & Dragons is spacious and comes complete with whole thieves guilds, secret wizard labs, and lots and lots of specially adapted monsters (like the Otyugh and the Cesspit Ooze).
Module I9 Day of Al' Akbar: The sewer under the city of Khaibar.
Supplement Adventure Pack I, adventure "The House of Long Knives". The sewers are 20 feet wide and 15 feet high.
Module A1 Slave Pits of the Undercity. The sewers under the city of Highport are 20 feet wide and 10 feet high.
Module FR1 Waterdeep and the North. The sewers of Waterdeep can be as large as 20 feet across and high enough for humans to walk through them.
Module Avengers in Lankhmar. The sewers of the city of Lankhmar are so tall that characters can walk upright in them with plenty of headroom overhead (approximately 8 feet high). They're also about 20 feet wide.
Dragonlance SAGA System supplement Palanathas. The city of Palanathas has sewer tunnels up to 30 feet high.
Warhammer is even worse: there are skaven, mutants, and chaos cults. The only solace is that all the shit is on surface.
Played straight in the first Gotrek & Felix omnibus, where the eponymous pair become sewerjacks (patrolmen, but for the sewers.) That's right, the sewers are so massive they require law enforcement. It's specifically noted that the sewers under the city of Nuln were made by master Dwarf artisans, and the system includes cathedral ceilings in some of the central tunnels.
Not surprising since they're based on the ones in Paris, but in 7th Sea, the sewer system in the city of Charouse in Montaigne is quite spacious and filled with surprises, including possibly a Stargate.
The Paris underground is complicated by the presence of a network of catacombs under the city.
In Shadowrun, the sewers under Denver happen to not only be rather spacious, but also open up to a maze of former subway tunnels and other cloaca, sites which attract communities of ghouls, rogue spirits, coyotes, and the occasional aspiring thaumaturgist.
This is actually rather common in Sixth World sprawls. Seattle features the Ork Underground, built on the old Seattle Catacombs, the bus tunnels, old basements, and lots and lots of sewer tunnels. Justified in the new Manhattan setting, where the city built right over the remains of an earthquake and just sealed off the old subway system in favor of suspended monorails.
In SLA Industries, the planet of Mort boasts a generously spacious sewer system, one vast enough to hide hordes of serial killer gangs and other monsters.
In Warhammer 40,000, the lowest levels of Hive Cities resemble this trope, and the lower decks of starships are about a fifty-fifty mix of Absurdly Spacious Sewer and Eternal Engine.
Justified in case of Hive Cities since it's stated many times that these mega-cities grow by new generations building on the ruins of the old ones. So those deep levels are actually remains of streets and buildings that have become enclosed on all sides, and therefore seem like tunnel systems.
Correction: According to Necromunda, it's the next-to-last levels of the Underhive that are like that. The very lowest level, a.k.a. "The Sump", is a literal sea of various human and chemical wastes, patrolled by diamond-eyed spiders the size of battle tanks.
Vampire: The Masquerade has sewers spacious enough so clans of vampires can live in them, along with libraries. So not only are they spacious, but dry.
Given that said vampires have covertly directed human affairs for thousands of years, one might think this trope justified there since one of the vampire clans prefers living in them.
As touched on a couple of times above, this trope can occasionally be justified in fantasy games by making the sewer system a series of sunken streets.
Chaosium's Thieves' World boxed set said that Sanctuary's sewers were large enough for armed troops to pass through them.
In Guys and Dolls, the New York sewers have enough room for a full dance number!
The sewers in Urinetown are large enough to hold the rebel "base". And one song with a full dance section.
As Urinetown is essentially a Troperiffic pastiche of musical theater, this is hardly surprising.
We never actually see the sewers per se in Les Misérables, as they're in most productions just represented by shafts of light that Valjean walks through, but everything is covered in Literature and Real Life.
A lot of videogames have this kind of level. For a more comprehensive list, look here.
Armored Core is a fairly egregious example: the sewers aren't just human sized, they are in fact mech sized. Combine this with the fact that the mechs in Armored Core are shown to be at least two stories tall, and that these sewers are spacious in relation to the ACs themselves, and these are some very spacious sewers.
Assassin's Creed: Altair's Chronicles features repeated trips through sewers with moving platforms and water that gushes out of pipes at repeated intervals for no apparent reason.
In true Batman fashion, Batman: Arkham Asylum reveals a massive complex of catacombs and sewer lines hidden in the deep caves of Arkham Island, one such system housing Killer Croc.
Many levels in the SNES and Mega Drive platform game Boogerman: A Pick and Flick Adventure.
Or at least the bonus areas, which are accessed by flushing yourself down a toilet.
The tutorial level of zOMG features this with a lampshade hanging in the in-game manual.
The Sewers of Draj.
Chrono Trigger: The Sewer Access in 2300 A.D., which you must fight and navigate through in order to reach Keeper's Dome.
City of Heroes: Paragon City has a huge sewer system choked with all kinds of villains (mutated cultist gangs, decidedly amoral surgeons and their scientifically animated zombies, just for starters...), and an abandoned network that's home to even more dangerous villains (extradimensional alien invaders, giant mutated monsters). Even generic missions have an instanced sewer map for this trope.
The Rogue Isles, in City of Villains, have their fair share as well.
Averted in the Praetorian Underground from the Going Rogue expansion — this insanely spacious tunnel system (complete with faction bases and offering an alternate way of getting from zone to zone fast) is not a sewer, but an abandoned subway network.
Along with vents and maintenance tunnels, a common way to safelynote for the most part get from point A to B in Deus Ex. One sewer junction has a bioweapons laboratory built into it.
The prequel, Human Revolution, continues this trend, to the point where hobos, street gangs and conspirators, make routine use of the sewers of Detroit and Hengsha.
One of levels in a Flash game, Dangerous Dungeons, is called explicitly "Absurdly Spacious Sewer".
The very first dungeon in Dark Chronicle is the sewers of the hero's hometown. While it is an easy level to blow through in less than an hour, it's notorious for being THE most frustrating area in the game to play the golfing minigame Spheda, due to the small gutters along the walls that like to trap your "ball".
Though perhaps cramped by video game standards, Diablo 2 has several underground areas that are far roomier than might be reasonably expected. Act 2 under the town and Act 3 beneath the jungle cities are two prominent sewer examples. And although not technically a sewer, the chapel basement of the original Diablo is absurdly larger than the building itself. . . even discounting the encroaching levels of Hell.
In The Elder Scrolls III: Morrowind, the sewers of Vivec are quite spacious with walkways on the sides and a deep waterway in the middle. Justified, since Vivec is a City of Canals, the sewers double as flood controls and the extra space is needed.
In the Tribunal expansion, the sewers are even more spacious. Justified once again, as the sewers are actually part of the original (destroyed) city which the current city was build over.
Justified in The Elder Scrolls IV: Oblivion. The Imperial City has insanely massive sewers, but it is explained in the in-game literature that the whole infrastructure is an abandoned Ayleid city, so the sewers apparently have just lost their former purpose.
Justified in Skyrim. The Thieves Guild operate out of a spacious sewer in Riften known as "The Ratways", though parts of it appear to have been originally built as underground warehouses and basements.
The plant life actually made sense in context since the sewers were also absurdly well-lit for no apparent reason.
Eye of the Beholder takes place, technically, in the sewers of Waterdeep. Though after the first levels, the sewer-ish feel is replaced by dwarven tunnels, drow mazes, thri-kreen hives and an underground palace.
Final Fantasy XII's Garamsythe Waterway is a labyrinthine series of tunnels that are at least thirty-feet tall and much wider. Some rooms are large enough to fit basketball courts, and these naturally, are the sites of boss battles. This is, however, heavily implied to be an actual waterway, designed for the purpose of bringing water into the desert city of Rabanastre.
Sewer areas in Glider PRO are just as tall as other kinds of rooms.
Several games in the Jak and Daxter series, particularly Jak II: Renegade and Jak 3, have levels that use this trope extensively.
Jet Set Radio Future features a positively palatial sewer system including vertical shafts several stories tall. (The player's choice of Rudie can skate right on up using his/her rocket-propelled inline skates.)
Knights of the Old Republic has one of these when you're searching for Zaalbar, the resident wookie. It's large enough to hide a Rancor in!
In Metal Gear Solid 3, Snake escapes Groznyj Grad the first time, after being captured, by tricking the guard into opening his cell, sneaking to a manhole in the base, and running through a sewer leading to an Inevitable Waterfall where he is confronted by Ocelot and the Ocelot Unit.
The Last Story has the party exploring several unexpectedly large underground environments, one of which is the sewers under Lazulis Island, which are aparently large enough to shelter the entire population plus leave plenty of dank monster filled corridors for our heroes to explore.
The Last Remnant has at least one example of this in the Nagapur Aqueducts, it is so spacious that Giants live down there.
Might and Magic VI has the Free Haven Sewers, VII has the Erathian Sewers. Both need to be explored for plot advancement and/or character promotion.
Postal 2 has a hidden one. It leads to a hidden Taliban base containing nukes.
Shadows of the Empire has a level where you have to infiltrate the Big Bad's palace through the sewers. There are some sections that are easily bigger than a football field.
Radiata Stories has Jack, the player character, traverse the sewers underneath his guild in a couple of missions. The missions are notoriously disliked due to the sewers also doubling as The Maze. Like Earthbound, the game averts the whole "not actually stepping in sewage" deal, to Jack's horror.
In Resident Evil 4, Leon falls through a trap door to a massive sewer system beneath Salazar's castle, complete with giant Plaga-cockroaches. Salazar compounds matters by sending his right hand to dispose of the protagonist.
'Your right hand comes off?'
Resident Evil 2 also had some absurdly spacious sewers, with features such as an elevating bridge and offices for sewer workers.
La Tale is notable for having a sewer that is several stories high.
The Legend of Zelda: Twilight Princess features one of these twice in the game: the same location appears as the training level for Link's wolf form, as well as later, after the third dungeon. While not a huge area, it's still absurdly spacious, and seems to double as a prison of some kind. It's also worth noting that said area is apparently inside Hyrule Castle, and clearly above ground level.
Of course, it's stated in game that someone's house used to be where the well is, so that level is presumably his basement. One can't help but wonder what the guy did in his spare time....
In LEGO Batman the Gotham sewers aren't just big enough to walk through; they're so big that you need a flight suit or a high jump just to reach certain parts of it. However, this network is not very well secured. Penguin and Killer Croc use the sewer system to break out Catwoman by coming up through the toilets in the police station. And yes, there are alligators.
Both Parasite Eve games with New York City sewers and a sewage passageway between the shelter and the motel.
In Portal, Chell travels through what appears to be an open-topped sewer... barefoot.
The video game of Robots has a mazelike sewer that is inexplicably set up like a huge pinball machine. You actually have to use a transport pod to traverse this level.
Romancing SaGa had two: Estamir and Melvir. The sewers of Estamir were catacombs that could connect North and South Estamir; had a graveyard, and a temple dedicated to a Stronger Sibling of the Big Bad. The Sewers of Melvir was a labyrinth that could allow one to enter the palace and had a temple dedicated to the Big Bad himself.
Sa Ga 2 has one in Venus' world. With MAGI and perfectly usable items, no less!
Serious Sam — The First Encounter and Serious Sam 2 have sewer levels. Lampshade Hanging in Serious Sam II when Sam says "I knew it! There ain't no games without sewer levels."
In Digital Devil Saga, the Anahata Waterways from the first game. Unlike most examples, this one doesn't need to have any explanation as to why it's so huge since the entire world is a virtual reality.
Sonic Adventure has Casinopolis' sewer, Dilapidated Way, which your ball gets dumped into if you lose a game of pinball. Sonic is the ball. Oddly, it's full of hazardous traps, money, shields and other things. However, subverted with Station Square's sewer, which is incredibly small and exists only to get Sonic and Big into the downtown city and Twinkle Park, respectively.
Sorcerer University of The Spellcasting Series has a large and complex sewer system beneath it, which Ernie must use for rapid and/or secretive transit. The tunnels are large enough for an elevephant to walk through without issue. Unlike a lot of video game examples of this trope, though, Ernie doesn't get the luxury of walking on nice clean ledges and pipes. The smell in some areas is said to be more than Ernie can bear, and occasionally, even more than a bear could bear.
Suikoden II has a traversable sewer area under Two River City, where a recruitable (and less-than-hygienic) character lives.
In Summoner, the sewers of Lenele are huge. Even great big Golems have plenty of room.
The Mario series frequently uses this for the famous underground levels. You could argue that the entire Mushroom Kingdom is a giant sewer system from the abundance of green plumbing pipes. In fact, the Ur Example for video games is the original Mario Bros., which is where the Mario Bros. themselves actually made use of their plumbing abilities.
Paper Mario: The Thousand-Year Door has Rogueport Sewers. Its massive interior is justified on account of it being the original ancient town that used to be there before its cataclysmic destruction led to it sinking beneath the ground.
Mario & Luigi: Partners in Time has one beneath Peach's Castle, though it's a fairly small example of this trope, as the only thing down there of real importance is Fawful's shop. The version seen under the Shroob-conquered version of the castle in the past is much bigger, however.
In Tales of Symphonia, Zelos takes everyone through the Meltokio sewer, which is spacious enough to allow giant rats to roam it freely, and has multiple levels, computers, and trash compactors.
And despite the trash compactors implying the area is normally used by workers, it can't be travelled without using a magic honey-we-shrunk-ourselves ring, walking on spider webs and patching up gaps in the walkways with blocks of garbage.
Team Fortress 2 — Anywhere there are sewers / underwater pipes, they're big enough for even the Heavy Weapons Guy to run and/or swim through without trouble. 2Fort is the most well known example, but other Absurdly Spacious Sewers can be seen in Doublecross, Hydro, Well, and a number of custom maps.
Toki Tori has Slime Sewers. The levels are covered in bright green waste and crawling with slugs.
Lots and lots of examples in the Wario Land series. The level Arabian Nights in Wario Land 4 for example has sewers big enough to fly a flying carpet through, and have various secrets hidden near the ceiling and under the water. Crescent Moon Village apparently has two separate sewer systems, both of which are much larger than you'd expect from the design of such a level. The Golden Passage in said game also has some kind of underground canal running all the way from the start of the level to the end, as some kind of place Wario lands in when he misses a jump.
In World of Warcraft, the city of Dalaran has a sewer area with spacious tunnels and halls that are big enough to contain several buildings and a small lake. There's even an inn down there! Other than said lake there's not much running water, and no waste other that some junk lying around in piles of rubble.
The Undercity is built out of the sewers and catacombs of the city of Lordaeron.
Both are justified: Undercity was in the process of being converted into Arthas' new throne when he had to leave and Dalaran's sewers intersected with their prison complex.
Lost Souls MUD has a couple of these, in the major cities of Losthaven and Liathyr.
The infamous sewer in Xenogears, where you can lose yourself eternally and forever and be assaulted by a giant mutated skeleton.
In Banjo-Kazooie, it seems like the entire of Clanker's Cavern is a massive, massive, massive sewer. To put it in perspective, the central room contains the level's eponymous whale-sized robot shark. Clanker's Cavern itself is accessed through one of the many similarly large sewers of Gruntilda's Lair (though they're comparatively small).
As befitting its tabletop source material, the sewers in Vampire: The Masquerade – Bloodlines are very roomy and connect to almost everywhere - luckily for those Nosferatu players who need to move around without being seeing by mortals.
Ratchet & Clank: Up Your Arsenal has a large sewer on Aquatos big enough for Ratchet, Clank, and Skid to break in, a multi-layered area hiding nintey-nine sewer crystals at twenty thousand bolts apart, and a humorously named weapons dealer of questionable credentials.
Comix Zone's sewers have enough room for our hero, Sketch Turner, to suspend himself from pipes to avoid low attacks.
The last section in Police Quest II. Which is sort of odd, considering that the games' main selling point is being so scrupulously realistic.
In Everquest II the sewers of Qeynos have vaulted ceilings so high and well lit that it practically looks like you're in a cathedral.
BloodRayne 2 has sewers big enough to do acrobatics in.
The future city of New Mombasa depicted in Halo ODST doesn't just have your average sewage system. It is also home to an extensive maintenance system that runs ten floors deep, an underground lake, dozens of Bottomless Pits, and a supermarket-sized AI construct.
Left 4 Dead has a pretty big sewer system in the third chapter of "No Mercy", aptly named "The Sewer." It's large enough for hundreds of zombies, a Tank or two, and has the space for a Smoker to easily launch his huge tongue at the survivors from a good distance. There are a few cramped ventilation ducts that you might find a Witch in if you're unlucky, but otherwise the actual sewers are pretty open.
Yoshi's Story features two levels set inside giant sewer pipes. The first level, Jelly Pipe, is loaded up with mysterious gunk that clings to the sides. The second, Torrential Maze, is full of rushing water to sweep you away.
When the heroes from Shining The Holy Ark get kidnapped they use a secret passage and escape into the sewers. It appear to be one massive space under a vaulted ceiling, with multiple levels, that is actually bigger than the castle above it. Maybe justified as there were more than one secret entrance to the castle and it's implied that soon of the royalty is entombed there...in the sewers.
Global Agenda gets in on the action with a mission in the subterranean waterways in North Sonara (Recursive Colony Update). It's the sort of spacious that some of the shorter-range turrets can't cover its width.
Neverwinter Nights: the player visits the sewers of Neverwinter, and, later, the sewers of Luskan; true to form, both of them more closely resemble a spacious network of extremely clean canals. The Neverwinter sewers even have bridges and a guy who lends you a boat.
Somewhat justified in Dungeons & Dragons Online. Most of the game takes place in city of Stormreach, built on the ruins of what used to be a giants' city. Sewers/storm drains date to the original city; they are spacious enough for humans and would just barely fit a giant.
A Dance with Rogues, a NWN mod, gives us the Betancuria sewers, which stretch under the entire city of Betancuria and are used as secret passageways by the local Thieves' Guild (even their main hideout is there) and as a Warp Whistle by the player. The sewers are large enough to host a plethora of monsters and a bunch of quests actually requires you to go there (or to be dumped there with no gearor clothes).
The Witcher has the Vizima sewers, which are large enough to house dozens of undead, a monster boss (which is, in fact, you very first mission mark in chapter two), and a whole bunch of conspiratorial meetings you get to crash in chapter three.
Yakuza 4's Saejima primarily gets around the city through traversing the sewer tunnels. It's pretty much the only way he can travel for much of the game due to being a wanted man.
In Dragon Age II, Darktown is an under-city that runs beneath Kirkwall, connected by old sewers and former mines, where the beggars and refugees that are too poor for even Lowtown have been forced to dwell.
The Sewers map in Perfect Dark multiplayer qualifies for this.
You briefly have to enter a storm drain in the Chicago level in singleplayer. What little explorable space there is happens to be quite large and open, aside from some small tunnels you have to duck to enter.
Twoson Sewers in The Halloween Hack. It's covered in hippies and rats. Varik enters this place to head for the monster's location. At one point, the water is replaced with blood, the hippies become zombies, and blobs and roaches join the fray.
In Kingdom of Loathing, the Hobopolis Clan Dungeon takes place in the sewers beneath Seaside Town.
The futuristic setting of Messiah has sewers big enough that an entire community of insane cannibals thrives in there.
In the Narbonic Director's Commentary, Shaennon Garrity openly admits that the design of Helen's sewer-based underground lab comes entirely from the old Teenage Mutant Ninja Turtles cartoon.
In Girl Genius, the sewers of Sturmhalten are not only large enough to walk around in, they're large enough to support a deeply alarming ecosystem. Sturmhalten is home to at least two Sparks, with it being implied that they're just the most recent crop. Once this is realized, the ecosystem — and the sewer system itself — starts to make sense. And besides that, the latest ruler of Sturmhalten had an alliance of convenience with the Geisterdamen — he was hiding them in a level under the main sewers. If there wasn't enough room for them to trek through and haul their Lady's equipment around with them, he would've redesigned things so that there would be. Although the comments from the two guides rather implies that the sewers have always been that way. Also, Sturmhalten is an old European town, and nothing in the series to date suggests that any of the European towns have modernized their sewer systems, although considering that said modernization would probably come at the hands of a Spark...
That's not unique. But deys not all as extensive as under Mechanicsburg. Or else Europa would collapse after a hard rain.
The sewer outlets are absurdly small compared the size of the tunnels inside, but the goblins do in fact complain about the smell and pass on eating the foodstuffs that were in their bags when they trudged through the sewage.
The Order of the Stick mocks this trope: Azure City not only has such sewers, but there are three tunnels clearly labeled "Ocean", "Anachronistic Sewage Plant", and "Obligatory Sewer-Themed Labyrinth".
Aversion: The Council team must navigate a proper storm drain that nominally catches rainwater from a nullah in the first story arc of Elf Blood.
The sewers of Rio in Vinigortonio are large enough to sail a boat down. Lampshaded by the characters
Jose Carlos: I had no idea sewers were so large!!
Vinicius: You'd be surprised at how much they hide from us.
Averted (not surprisingly) in Freefall: Sam is planning to infiltrate the Ecosystems Unlimited but is forced to abandon the sewer route. Not because he couldn't use it, but because Florence isn't too excited about the thought of having to remove a few bones from her body to fit through the ten centimeters narrow pipes. Sam himself doesn't haveany bones so he could technically do this.
A sanitary sewer like this appears on the island used for version two of Survival of the Fittest, spanning the entire island underground, but from the vague descriptions it's implied that people can only just barely move across the walkways on the sides, and that otherwise it's fairly cramped.
The sewers of The Town are also infamously large, spacious and full of random monsters including rat shaped robots and Xenomorphs.
In the story "Boston Brawl" in the Whateley Universe, the Boston sewers are big enough to get lost in. Phase gets stuck in the pitch dark, knee-deep in.. ugh, don't even think about it. Then she gets attacked by hundreds of The Necromancer's zombies. In the pitch dark. Ick.
In "Merry Meet, Merry Part, and Merry Meet Again", Merry spends a lot of time in the city sewer to try and keep out of sight - and then ends up going deep enough that she finds a man-made cavern with a very powerful computer hidden inside. The reasons for this, and what else is hidden in the cavern may qualify for a partial AI Is A Crap Shoot. Or possibly a subversion thereof, since Palm was deliberately going for humanity-unfriendly AI.
These have appeared in several Global Guardians stories, but they are always storm drains and flood-control tunnels, old abandoned subway lines, and other tunnels people were meant to access rather than sanitary lines. The most notable case was when Team America discovered the Twelve Tribes living in the catacombs under New York.
Partially subverted in Catacombs of New York. The sewers there are approximately the size that the real sewers of New York are, until you get to the buried underground Indian settlement.
In Mother Of Learning, many town sewers are made out of sealed-off parts of The Dungeon, an enormous underground maze of tunnels.
In Curveball, Farraday City's sewers were apparently built specifically for people to travel through — complete with secret rooms for the travelers to hole up in. Later on, we find out that the water that flows through them during a storm forms a magic rune the size of the entire city.
Futurama really played with this one in a few episodes. New New York's sewers are actually the city of New York, and home to a community of mutants, who mention off-hand that they have a sub-sewer system (home to a community of sub-mutants, according to sub-urban legend). It helps that New New York's sewers connect with the subterranean ruins of old New York. Reality intrudes, however, when the Planet Express crew gets lost down there and Fry says that the only way out is through... a tube that's at most only a few inches wide ("Don't worry, it gets wider after about a mile").
Teenage Mutant Ninja Turtles. In all incarnations, their sewer lair is larger than any house you've been in (possibly) and the tunnels are wide enough to accommodate vehicles like the tank-sized Battle Shell. It is very seldom that the Turtles must come into contact with anything you've flushed. In the 1990s cartoon, their original lair was invaded and they later got another, even more palatial one.
Kind of justified; Their second lair was actually an ancient, abandoned Elyntian outpost. They later moved out of the sewers and into a pumping station.
Averted in the most recent series due to their lair being a subway station as oppose to the sewers.
Mainframe in ReBoot was shown to have sewers in one episode. Why digital lifeforms require them is a mystery.
They're for when someone calls flush();
In Sonic Underground, the only way to get very deep into Dr. Robotnik's empire was in... the sewers.
Avatar: The Last Airbender : When the gang needs a way to sneak into the newly-occupied Omashu, Aang shows them a secret way through the sewers, which is large enough to hold nearly the entire population of the city. More realistic than most, given it's full of sticky smelly goop that Aang and Katara are able to bend away from them, but that Sokka gets covered in - and gets a little too closely acquainted with some of its denizens as a result.
Kim Possible has done the sewer gig more than once, even twenty years into a dystopian future. In their defense, they actually had to walk through some of the sewer fluid.
Freakazoid! used this until it became a running gag, with more than one character complaining about "poo gas".
One characterRoddy McStew notes they're called "crud vapors" in his native Scotland.
Several villains in Batman: The Animated Series based themselves in the sewers, requiring Batman to go there in search of them, like the Sewer King and his legion of children, and Killer Croc. The Penguin also briefly had a hideout in one, likely referencing Batman Returns.
Likewise, Batman Beyond ventured into a downright cavernous sewer system in at least one episode.
In The Tick, Sewer Urchin lives in an enormous apartment in The City's sewers, and on some occasions provides the other heroes with goods that are otherwise difficult or impossible to acquire, claiming "You'd be surprised what people throw away, yeah, definitely."
In The Spectacular Spider-Man, Flint Marko and Alex O'Hirn flee the scene of a robbery by busting through the store's basement wall, and escaping into marvellously cavernous sewers, only to be promptly caught by Spider-Man. Later, Spider-Man traps the Rhino in a steam-tunnel created from ruptured sewer pipes. Quarters are tighter, but the hulking Rhino can still maneuver relatively freely. Half the Sinister Six persue a fleeing Spidey through these sewers as well.
In an episode of Hey Arnold!, Arnold drops his grandfather's watch down a hole to the sewer (which somehow didn't break even though it fell for three seconds before hitting the ground: a drop). He descends into the sewer to retrieve it only to find it has been taken by the "Sewer King," a man who lives in the sewer and claims sovereignty over it.
Stock Animation in Code Lyoko often has the heroes skateboarding through some very spacious sewers. Then again, the series is French...
Since the water is flowing directly into the river, it is more of a storm drain tunnel than a sewer.
In Ed, Edd n Eddy, the sewers beneath the cul-de-sac, as seen briefly in "High-Heeled Ed" and more extensively in "Boom Boom Out Goes the Ed", are pretty spacious.
The Family Guy episode "Breaking Out is Hard to Do" ends in a sewer that is wide enough to fit two TIE fighters.
Notably averted in the The Shawshank Redemption parody, where Peter barely squeezes through a half mile of dirty sewage escaping.
Danny Phantom had one episode where the sewer system was big enough to support one ghost boy, his currently possessed love interest, and thousands and thousands of big ass vines gunning towards him. Has some incredibly clean water, too.
The small town of South Park even has spacious sewers big enough for the boys (and Mr. Garrison) to walk in when searching for Mr. Hankey in "Chef's Chocolate Salty Balls." Obviously, the presence of a magical talking piece of crap means the "no poop" rule is averted.
Even ignoring Mr. Hankey, the show is one of very few works to acknowledge the disgusting nature of sewers in general. In one gag, Cartman sneezes on Kyle, who complains that sneezing on others is gross and unsanitary. Cartman responds, "oh, sorry, you wouldn't want to get exposed to germs while you're knee-deep in human feces."
Arlen sewers in King of the Hill episode "Serpunt" is big enough to walk on when Dale and Hank hunt down the escaped snake.
The Simpsons episode "Two Bad Neighbors" has walkable sewers running perpendicular to the street when Bart and Homer attempt to sneak into Bush's house.
Total Drama World Tour has one of these in the episode "Broadway Baby". The cast rides speed boats through it.
This seems to be the deal with the sewers of Mellowbrook on Kick Buttowski as Kick manages to operate them quite well, even with Kendall riding with him on his skateboard. They also appear to host crocodiles or aligators.
Phineas and Ferb have this when Candace is required to battle a sewer-dwelling aligator/crocodile to get one of her Fire Side badges.
During the song "Subterranean Crocodile Apprehension Expedition", the usual gang along with Irving and the Fireside Girls, all of them riding a total of 4 jet-skis; try to chase Candace and a crocodile, both in an airboat; doing a race on the sewer rivers that include several tunnels, water curves, crossings and sidewalks wider than a truck. It even has a ladder up to the subway stations and the subway railway itself.
The sewer in the Talespin episode, "Bringing Down Babyface" is (just barely) big enough for Baloo to fly his plane, the Sea Duck through.
The sewers of Bayville in X-Men: Evolution are fairly sizable, large enough for characters to more or less walk upright in most places, but in most circumstances the characters have to walk through the dirty water. Still a big enough space for a camp for the Morlocks to live in, though.
Truth in Television for almost any city of significant size, although what most people would consider "sewers" are actually storm drains that are for carrying excess rainwater away from the city to prevent the streets from flooding.
London's sewers are in places as spacious as computer games would suggest, having been built on a massive scale in the 19th century to accommodate future population growth (though the network has grown a hundredfold since then). The Victorian-era section of the London sewer system is huge, with several million tons of brickwork and tunnels up to nine feet in diameter. There are also many kilometers of unused underground tunnels built for other purposes, ranging from railways to military bunkers.
Some old cities have large underground cisterns, design to collect and hold rainwater, which reach the sizes of some of these fictional sewers. For example, the Basilica Cistern in Istanbul.
Truth in Television: There are whole communities living underground in New York City and Paris, to name a few, and obviously, there's more than enough elbow room. In Paris, there are even illegal theaters and passageways to the catacombs via sewers.
Many of the much older major cities, especially the ones in Europe, have vast underground networks of tunnels and rooms that are leftovers from the city's previous development age. For example, Rome is built over many ancient buildings, Berlin has numerous World War II era bunkers, and Chicago has a labyrinth of secret rooms and passages built during Prohibition.
The parking lot in front of Baltimore's City Hall has the old Jones' Falls River Bridge buried under it. When the river was moved to build Downtown, whoever was in-charge decided to bury the bridge instead of tear it down. This has the unfortunate side effect that as much as the city would like to sell the land for another skyscraper, they can't because the bridge protects much of the main sewer, water, and electrical lines running through the area (making it too expensive/inconvenient to remove) and with the bridge there it destabilizes the ground and any potential foundations laid there.
The Brussels Premetro (tram line which goes part underground like a subway under modern Anspach Boulevard) runs in a former riverbed which had become an open sewer in the 19th century and later got drained, covered and built upon.
Not technically a sewer, but Toronto's path is made up of numerous underground tunnels and walkways, often housing retail stores, connecting many of the major office buildings downtown and linked to the subway system.
Even moreso with Montreal, which has a of tunnels/underground complex doubling as one massive shopping mall spanning most of downtown (The so-called "Ville Souterraine", or "Underground City" to Anglophones, is the largest underground complex in the world). Built because the extremely harsh winters tend to drive pedestrian indoors.
Rochester, MN also has an underground walkway network that serves a large part of the city. I believe this type of infrastructure is common in cold cities.
Further, there are sections of both Toronto and Montreal's sewers that you can walk comfortably in standing upright. People have done it (and gotten arrested), but it is definitely large enough to fit a man standing upright.
Osaka, Japan has a network of pathways which connect several of the subway stations. The subway stations in Tokyo could count in their own right: several are huge sprawling complexes where multiple subway lines cross. Sapporo has a pedestrian tunnel system under the inner city measuring 1.7 kilometers from north to south and 1.1 kilometers from east to west.
Seattle had a major fire in 1889, and to make sewage flow out into the sea (at high tide, it had a habit of... going the other way from outhouses) they simply rebuilt everything on top of the old foundations. That means today there is a sort of small town buried beneath downtown's streets. Highly unsafe in most of it though.
In Cologne there is a huge hall with two candelabra in it. It was build for a visit from Kaiser Wilhelm II 
In the Warsaw Uprising the quoters separated by Nazi forces tried to communicate with each other using the sewer system. It could be described as anything but spacious and clean. In one case a whole quoter (both soldiers and civilians) was evacuated by these means.
The street level of Atlanta is today one story above where it was a century ago, due to a system of viaducts built to raise it out of the way of the railroad lines. When the lower level was "rediscovered" in the 1960s, it was turned into a shopping and entertainment mall. (What else?)
Texas A&M University has the "Steam Tunnels", a system of underground utility tunnels under the main campus originally built to pump steam from a central plant to the various buildings' basements to heat them during the winter months. Now it is used to run water and sewage pipes, electrical and phone lines, and network lines. Campus lore says that there used to be a few student "lounges" set up in intersections of the tunnels where there was a bit more space, but nowadays the access grates to the tunnels are padlocked, and exploration of the area is discouraged by the university officials.
The University of BC in Vancouver has a similar system, but they're still easily accessible if one knows how. However, nobody goes into them but repairmen and engineering students mucking around.
Chicago has the Deep Tunnel project, which is a pretty massive-scale water handling project that includes storm flow as well as sewage. Some of the tunnels are easily wide enough to walk through, and it's even possible to get to some of those areas via manhole.
While not a sewer, and certainly not as extensive as the other examples on this page, Quebec city's Laval University has built a tunnel system under it's campus to link every buildings. A student could theoretically pass the whole year without ever needing to go outside, as almost every kind of services and store are available in at least one of the university's building.
Lakehead University in Thunder Bay has a similar system of tunnels (both public access and service) for the same reason; it gets really cold in the winter. Sadly, the university has outgrown the public tunnels and only the main buildings are connected, making for a chilly walk to some classes or back to the campus residences.
Harvard University has fairly extensive tunnels, though their accessibility varies depending on the building you're in. In some cases there are sections of buildings (like the philosophy section of the Widener Library stacks) that can only be reached through the tunnels.
Most older large university campuses have a fairly extensive network of tunnels underneath them, generally built to pipe steam from the main physical plant to other buildings (it's cheaper and more efficient to build and run one enormous boiler, or even several smaller ones in a single location, than separate ones for each building). The tunnels were made large enough for maintenance workers to access and repair the pipes if necessary.
Recently-deceased fugitive Raoul Moat evaded capture by the police in Northumberland for eight days, apparently by hiding in Rothbury's network of storm drains, popping out of manhole covers occasionally to steal vegetables from allotments, and for a stroll in the High Street.
St. Louis, MO has a fairly large underground made up of sewer systems, old railway tunnels, various tunnels for other purposes, and lots and lots of caves (that have been mostly sealed off). Very few people (if any) in the city know exactly how extensive they all are and it is very illegal to go down into them, and for good reason. The sewers, tunnels, and caves are so full of toxic gas build up that going down into them without a copious amount of protective equipment is practically suicide, and that's assuming a collapse doesn't kill you (since the older ones aren't exactly easy to maintain).
Most of the outer suburbs around Detroit have no sanitary sewer system; wastewater goes into septic tanks and runoff goes into a network of drains and lakes. Most of these drains are above ground and some of them are basically artificial rivers over 10 feet wide and 6 feet deep.
Mexico City is a city suffering subsidence (sinking of buildings) at a rate of 30' per year (a lot), including their old sewage system, which is starting to flow back on itself as a consequence. Their sewage system is old fashioned in that it combines all of the sewage, instead of having separate drains for hospitals, industry, etc. To cope with this, they are currently building a huge sewage pipe which will be several meters in diameter and be able to pipe out 450 million liters of sewage per second.