Secret Underground Passage

Don't worry, there's only about a 50% chance of finding some sealed away horror down there.

"Not more than one secret room or passage is allowable, and such a passage may only be in a house or building for which it is appropriate by age or purpose."

— Father Ronald Knox, "Ten Commandments"

Often discovered by a snooping hero, the Secret Underground Passage is a popular trope in mystery and adventure-themed works. They are often a secret way of going from point A to point B without being detected, usually built into houses or castles. If bad guys built it, then the Secret Underground Passage is often used as a place to smuggle things and stash loot, or hide prisoners. If good guys built it, it's often a place to escape persecution, sneak past danger, or hide something important they don't want the bad guys to find.

Characters may also use a passage to hide the arrival and departure of a secret lover, an undercover operative, or a shady informer.

Secret passages are popular in detective fiction, as they can enable the murderer to move sleathily between rooms or even to get outside undetected.

This is sometimes discovered when the hero notices strange sounds - often human voices - and tries to find their source. Other times, it's discovered simply by accident when poking around, or even just leaning on the correct bookshelf and conveniently revealing the hidden passageway.

Sometimes the Secret Underground Passage is not just a single passage, but links to a huge network of tunnels under the ground.

A staple of Dungeon Towns. Compare Absurdly Spacious Sewer. Subtrope of Secret Path. Supertrope of Bookcase Passage.

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Examples:

Anime & Manga

• There are at least two in Corsair, one beneath Sesaam's bed that allows Canale to escape after murdering him and another in one of the rooms of the D'Aubigne mansion, which Canale uses to rescue Aura.
• There's one in Detective School Q, where they found out all this while that their school building has a secret passage. Once there, they find what seems to be evidence of a person imprisoned underneath, with a diary written in his own blood.
• In Übel Blatt, Koizell and Ato use an ancient subterranean passage to cross under the mountains so as to avoid Glenn's armies, but Glenn suspected that the notorious "Hero Killer" might possibly know of the secret tunnel although it seemed very unlikely.

Board Games

• Clue provides two as quick ways to access the opposite corners of the board. It also prevented a single unscrupulous player from blocking you inside a room by standing right in front of the only door out of those corner rooms.

Comic Books

• The tunnel connecting the garage in the Bat-Cave to the roads into Gotham in the various Batman incarnations. Whether this is a Tunnel Network depends on the writer as always.
• Von Goosewing made one into the castle of Count Duckula. Of course, it wasn't a very secret passage - Igor and Duckula figured out what he was up to long before he finished, and occasionally entertained themselves by watching him dig.
• In Prince of Persia: The Graphic Novel, there are secret passages connecting all the wells, new and old, known only to the Guardians of the Waters.
• Sleepless has one that connects to the various secret passages that crisscross the halls of Harbeny's ancient castle — the underground portion is built into a series of magically concealed caverns beneath the royal catacombs that lead out to the nearby coast.
• Steelgrip Starkey and the All-Purpose Power Tool has an underground tunnel near the New York Public library leading to the Star Key Enterprises headquarters.
• One is dug over several issues of Revival by the militia to undermine the quarantine.
• Wonder Woman Vol 1: Hypnota's villain lair is hidden in a series of interconnected underground passages with the entrance disguised as an old tree stump.

Fan Works

• All For Luz: At the back of the Porter family house is a staircase leading to the entrance of The Underdark: an Underground City founded by Gus's father. Its roughly around the same size and layout of Bonesborough that has been built over the course of 14 years right under Emperor Belos's nose.
• Shadows over Meridian: The Sand Dweller settlement of Shallowsands is revealed to have been built around the entrance of an underground tunnel leading to Cavigor. Originally a maintenance tunnel used to make the construction of the subterranean prison easier, it was magically sealed by the contemporary queen and forgotten once the prison was completed. As Frost's army besieges Cavigor, a reserve force digs the tunnel open and enters the prison while the main army launches the final assault, ending the siege in Frost's favor.

Films — Animation

• In Madagascar, the penguins are introduced digging a tunnel to escape from the zoo. In the Spin-Off The Penguins of Madagascar, it's revealed that they have a network of 15 escape tunnels.

Films — Live-Action

• National Treasure 2: Book of Secrets has the main character take the president through a secret underground passage in search of answers to a historical mystery.
• Snow White & the Huntsman. Snow White and her knights in shining armor are riding on the Queen's castle, which is on an island and so can only be attacked in the short time the tide is out. Cut to the dwarves sneaking in through the sewers.
  "We're promised gold and what do we get? Poo!"
  "Eww! I think that's one of mine."
• The house in Clue has the same two as in the board game. Both are used in murders: to escape the kitchen after killing the cook, and to enter the lounge to kill the motorist.
• Involved in one of the It Was Here, I Swear! gags in Abbott and Costello Meet Frankenstein.
• In Avengers: Age of Ultron, Tony finds one of these when investigating Baron von Strucker's lair. Judging by his attitude after discovering it, he was anxiously expecting one.
• Averted in the 1975 movie Operation Daybreak (aka The Price of Freedom). The commandoes are hiding in the crypt of a church which is surrounded by German troops. They try to locate a hidden passage they've been told is there, but their information is wrong and those who aren't killed in the fighting choose to commit suicide when the Germans flood the crypt to force them out.
• In The Phantom of Crestwood, Frank makes a throwaway remark about the house being riddled with secret passages: a relic of the days when his ancestors had to worry about revolutions. Dan and Pete later discover a secret passage running from the cliff to the cellar, and a second passage plays a vital role in the killer's final plan.
• In Ask a Policeman, a tunnel leads from Devil's Cave to the cellar of the police station, which the smugglers use to transport their contraband from the beach to the village.
• In Mercenaries, there is a secret passage leading from the Citadel to the church in the village. Fortunately for the team, Mei-Lin reads Cold War Architectural Digest.
• In Henry's Crime, Henry discovers there is an old bootlegger's tunnel running from the bank to the theatre across the alley. He plans to reopen the tunnel and use it to rob the bank.
• The 1952 Film Serial Zombies Of The Stratosphere has the Martian hideout accessed via a hidden trapdoor ladder in a flooded mine shaft, which they can access due to their superior Martian swimming skills. The hero Larry Martin is nearly killed on several occasions when he goes snooping around there, but instead of calling in a squad of Navy UDT's to do a proper search, he waits until the final chapter when Leonard Nimoy's character finally tells him how to get inside.

Literature

• Camp 30: The German prisoners are revealed to have been digging one that extends 300 kilometres outside of Camp 30 as part of the Great Escape that George and Jack were trying to foil.
• In Harry Potter, Much of Hogwarts castle is built with several secret passages that the students use to get around school quickly. The castle has so much and some are so well hidden few people know the exact locations of each one. The only three plot significant secret passages used in the books are passages leading into Hogsmeade Village:
  • One leading to the cellar of Honeydukes candy store.
  • Underneath The Whomping Willow into the shrieking shack.
  • The portrait of Ariana Dumbledore in Aberforth's home leading to the Room of Requirement. This last didn't exist until Deathly Hallows, and was created by the Room of Requirement.
• The Radix has two: one in Prince Zaki's residence, another in Carl Jung's castle.
• In Nightrunner, there's one in the fourth book leading from the workshop out to a barn.
• The Castle Canyons are secret passages in the Castle of Septimus Heap. They are used by Jenna, Septimus and Marcellus Pye in Darke to get around while the Castle is swamped by a Darke Domaine.
• In Feliks, Net & Nika entire sewer system of Warsaw becomes one when Golem Golem escapes into it. Those are Absurdly Spacious Sewers and many of them run next to basements. Golem Golem, being massive robot, just punches through whenever he wants to enter someplace.
• Pyrates is made of this. There's a secret underground path beneath the family home, which has been in existence for centuries. A great deal of the book takes place underneath New York City, and the underground paths lead to several places including the bad guys' hideout, and different parts of NYC.
• The Ghost at Dawn's House in The Babysitters Club series. Her house was built with a secret tunnel (with a secret panel in her bedroom wall) to assist people on the underground railway.
• There are a few in Alexandre Dumas' The Three Musketeers series. In a footnote to the Oxford World's Classics edition of The Vicomte de Bragelonne, editor David Coward remarks on the historical accuracy of one such passage:
  There was a communicating tunnel in Fouquet's town house, but not at Saint-Mandé. But Dumas was not a man to waste a good subterranean passage.
• In the last chapter of The Extraordinary Adventures of Arsène Lupin, Gentleman-Burglar, Lupin discovers a hidden underground tunnel between a house and a nearby church, and uses it to abscond with the furnishings. Secret underground passages also occur in other Lupin stories.
• The Adventures of Archie Reynolds has one used by smugglers, that the heroes stumble across while exploring the neighborhood.
• Beowulf has a secret underground passage into the dragon's lair; a thief uses it to steal a goblet from the dragon's hoard while the dragon is sleeping, causing the dragon to go on a rampage when it figures out that it's missing.
• The Hobbit has a secret underground passage into Smaug's lair; Bilbo uses it to steal a goblet from Smaug's hoard while Smaug is sleeping, causing Smaug to go on a rampage when he figures out that it's missing.
• A popular stock trope of British children's mystery/adventure author Enid Blyton.
• In the Warrior Cats series, there's a culvert under the road in ShadowClan territory that is considered by the cats to be a secret passage; it can be used for safely crossing the road and for sneaking onto the other Clan's territory. ThunderClan didn't know about it for years until Fireheart and Sandstorm discovered it.
• In Vernor Vinge's novella, "True Names", the castle in the Other Plane where the Coven meet has only one well-guarded way to enter, but, as Erythrina reveals, it has secret passages that can be used to leave. This being virtual reality, making them one-way is not difficult.
• In Andre Norton's Ice Crown, the gates of the queen's city are closed. Nelis, however, knows of one of these.
• The Executioner.
  • In "Stony Man Doctrine" the terrorist Psycho for Hire assassinates his KGB handler, who lives in a guarded compound, by entering via the one place not covered by guards and security sensors — the secret escape tunnel. If guards are posted on the tunnel it could lead to Bodyguard Betrayal. Likewise an alarm sensor would eventually be activated by rats or rainwater, again giving away the location. The engineer who designed the tunnel was transferred to another part of the world so he wouldn't reveal the secret, but the terrorist tracked him down and bribed him with gold to start a new life in the West.
  • In "Canadian Crisis", Bolan discovers a network of passages and hidden doors built into the walls of a Montreal hotel. He uses these to wage guerilla warfare on a Mafia conference being held there, and eventually finds out that the passages were put in during construction by Quebec nationalists planning a terrorist attack on dignitaries who would be staying in the hotel during the upcoming 1976 Olympics.
• In The Girl from the Miracles District, there are two:
  • There's a tunnel beneath the street connecting burlesque theatre Music Box with bordello Terra del Fuego. The two establishments are owned by twins, and because "private shows" with the girls are not allowed in the Music Box, the clients who would like them but can't or shouldn't be seen entering Terra del Fuego use this way.
  • There's another secret passage between Order HQ and the house of its leader, Irena, put in place so that no-one could track down where she lives by stalking her, and also so that she could escape quickly if need be.
• Friday. Friday stays with some friends at their Big Fancy House, which has a secret room plus escape tunnel in case they're raided by the authorities. Later when she's on the run and realises she's close to their house, Friday has to work out where the passage is (and evade its defenses) from what they told her.
• Watership Down. The 'slack run' was dug by the rabbits as a means of coming up behind some enemy and attacking them. When the warren is destroyed by men plugging the runs and filling the warren with Deadly Gas, a couple of rabbits use the slack run to escape.
• In the footnotes to Pale Fire, the king of Zembla triggers a secret door to escape from his house arrest and travels through a secret tunnel that goes out of the castle, enabling him to flee to the countryside.
• It's revealed in Yours Truly that the Lovejoy house has a secret tunnel in the Secret Room under the stairs. The original Truly Lovejoy used it in her Underground Railroad efforts until it suffered a cave-in in 1862.
• Spinning Silver: The present-day Duke of Visnya built an escape tunnel out of the Jewish Quarter, having won the city by conquest and fearing he could lose it the same way. Miryem's grandfather found it and keeps it as insurance against an anti-Jewish pogrom. The Duke uses the tunnel to seal away the Staryk King, which the grandfather again guesses and informs Miryem of.
• In The Secret Life of Kitty Granger, the Orchestra suspect that Nazi sympathizer Henry Lowell has a Secret Room in his estate where he and his cronies make their plans. Kitty and Verity are sent undercover to look for it. Sure enough, Kitty finds a hidden door in the wine cellar that leads into a passageway that leads to a chamber where Lowell, Smythe, and their friends plot their False Flag Operation and their takeover of the British government.
• Star Wars Legends: In the X-Wing Series novel "The Krytos Trap" there are a number of secret passages from Isard's buried Super Star Destroyer Lusankya to various locations on Coruscant. Included in the locations were an old Senate sub-committee room and an unused room in the galactic museum. Corran Horn is able to use the galactic museum passage to leave Lusankya and go to the galactic museum, and from there make his way back to the New Republic.
• The Magician's Nephew: A rare above-ground example. The plot begins with the children exploring a tunnel which goes through the attics of several houses, and they enter what they believe is an empty house, but is in fact Uncle Andrew's attic study.

Live-Action TV

• Arrow. In "Monument Point", Oliver Queen sees a shelf of archive boxes in the basement of City Hall. The papers on the bottom shelf are fluttering from the air passing under a hidden door leading to HIVE's Underground City.
• Sweet Home (2020): The survivors inadvertently discover one near the makeshift gravesite. They use it to escape the building when it's under siege by the military, who believe the survivors are armed and dangerous.
• In the Doctor Who serial "Genesis of the Daleks" there is a secret underground tunnel between the Kaled and Thal cities that Davros uses to sneak the newly created Daleks into the Thal city. This leads to a bit of Fridge Logic. If the Kaleds knew there was a tunnel between the two cities, why didn't they use it to smuggle normal troops into the Thal city and end the war years ago?
  • However when trying to get back to the city Sarah and Harry are attacked by Mutants, showing that it is still a dangerous trek to get to the tunnels and that it would be difficult to get an army there.
• On Leverage, this occurs during the 10 Lil' Grifters Job. It is how the killer gets away and frames Nate. It's also where the blueprints are hidden.
• Game of Thrones. In Season 7, Tyrion Lannister sends an army to besiege Casterly Rock where he grew up. Normally this would be a costly affair, but it turns out while his father trained the Lannister army and built the castle's defences, he put his least favourite son in charge of the sewers, where Tyrion built a secret passage so he could smuggle prostitutes in without his father noticing. A small force enters the castle and opens the gates from the inside.
• The Avengers (1960s) had some fun with this. Emma Peel in a fetish outfit is being whipped by the Villain of the Week, but his whip catches on a torch pulling it out of the wall, and activating the requisite trapdoor which he falls into.
• Married... with Children: Al and Jefferson built a tunnel in Al's basement only to be used in case of emergency... which leads straight into the Nudie Bar.
• Ripping Yarns: In the episode “Whinfrey's Last Case”, the titular hero is imprisoned by the spies he has discovered in a coastal inn. However, as this is a parody of classic adventure fiction, the inn is inevitably an old smugglers’ haunt, and it is basically impossible to walk across the room without triggering the entrances to a couple of secret passages.
• Titans (2018). In "The Asylum", our heroes try entering the eponymous asylum via tunnels to the decommissioned outbuildings, enabling them to get past the sentries patrolling the grounds. It's no surprise the enemy is waiting for them inside the tunnels, and the gas lines that run through the tunnels prevent Starfire from using her powers without blowing them all up.

Pinballs

• In Williams Electronics' White Water, there's a small and barely-visible passage near the top of the table, under the upper playfield. It's usually only accessible via a soft shot up the left orbit, and making it automatically advances the player's raft.
  Willie: "You found the Secret Passage!"
• The Pink Panther pinball has a Hidden Staircase and a Secret Passage; they are used to lock balls for multiball.

Video Games

• In Dragon Age: Origins, there's one between the windmill and Redcliffe Castle, used by the generations of Arls of Redcliffe as an escape route for their families in case of a siege. In the game, the Player Character uses it to sneak into the castle, however. Later on, in Dragon Age: Inquisition, the Redcliffe Castle is taken over by a Tevinter Magister, so (if you decide to pursue this story branch), Leliana—a former companion of Origins' PC—smuggles a cadre of her agents inside via the same underground passage.
• There's a number of these in The Legend of Zelda series. The most noteworthy are the tunnel leading from Hyrule Castle to the Sanctuary in A Link to the Past, and another series of passages leading from Hyrule Castle Town into Hyrule Castle itself in Twilight Princess.
• In Call of Cthulhu: Dark Corners of the Earth, an old smugglers' tunnel is the route through which the army attempts to get into an otherwise inaccessible building. All the soldiers die, and the player is the only one left to go through them.
• Underground train tunnels and subways, sewers, and bunkers in the Fallout series.
• The secret underground tunnels in Umineko: When They Cry were, in the spirit of Knox's 3rd, historically and plausibly justified. These are never involved in any of the closed door mysteries.
• A staple of the Nancy Drew series.
• The Myst games have these in spades. Helps that the D'ni civlization behind some of them lived underground to begin with.
• A variant of this is the basis for one of the side-quests in the Original Campaign of Neverwinter Nights. If you talk to a child standing outside a certain house, she tells you about a secret passage in her house which opens when a certain word is said. Overlaps with Open Sesame.
• In Quest for Glory I, you have a secret passage used by two members of both the Brigands and the Thieves' Guild, that the Hero can use to get easy access to the fortress. You also end up using it as an escape route.
• In Quest for Glory IV, there is yet another such passageway initially intended as an escape route from the Castle that leads to the graveyard, but you can use it to get easy entrance later in the game.
• In The Elder Scrolls series, the Imperial City (capital of the various continent-spanning empires in Cyrodiil) is built above the ruins of an ancient Ayleid city. Some parts have been converted into sewers and dungeons, but secret passages into this area are plentiful. You first escape through it during the opening level of Arena, after you were imprisoned by the Big Bad (although you wouldn't have gotten far if a ghostly guide hadn't pointed you at a portal hidden in the tunnels capable of taking you half a continent away). You find yourself back here in Oblivion, where you start as a prisoner in the Imperial City dungeons. However, your cell (which is supposed to be kept empty) has a secret passageway into the sewers. The Emperor and his bodyguards, escaping assassins, need to go through your cell to escape where you can tag along. (It helps that Emperor himself has seen you in a Prophetic Dream.) You can return once again in a later side-quest, where you'll need to sneak back into the dungeons through the underground passages in order to assassinate another prisoner.
• Prayer of the Faithless: It's how Aeyr's group enters Verigo Castle, when they have to enter.
• Resident Evil has an entire underground network of tunnels that connects the mansion's garden area to the underground laboratory. The entrance to the underground is concealed by a waterfall.
• The hidden dungeon beneath Chief Iron's office in Resident Evil 2 has an underground passageway that connects the RPD to the sewers. Said sewers lead to Umbrella's laboratory. Chief Irons would use these passageways to meet with William Birkin.

Web Comics

• In The Beast Legion Master Surya reveals an underground passage to the anointment room in Issue 5
• Cornucopia: The Palace of Sugars has one of these, leading from the dungeon to the bathroom.
• Keychain of Creation breaks down exactly why some of Tolkein's ideas on secret doors were actually pretty bad.
• Girl Genius
  • Sturmhalten's deep down, beneath it's spacious sewers, is full of secret passages and used to be frequently traveled by official Sturmhalten sewer rats (explorers who kill loose monsters) but was closed by the Prince supposedly due to it becoming too dangerous though it was more likely to hide the fact that he was providing a large contingent of Geisterdamen a shelter and room for research down there.
  • The "sneaky gate" in Mechanicsburg leads to a passage underneath the town which the Jägers use as a loophole to get to Mamma's before the Doom Bell rings since they technically haven't entered Mechanicsburg itself.
• Unsounded: The old mining tunnels beneath Ethelmik are not exactly secret, but few know how to traverse them and as the town is dying smugglers take advantage of them and Ethelmik's location on the border of Cresce.

Web Original

• Dice Funk: Rinaldo looks for a secret passage in every building. He has yet to find one.

Western Animation

• The secret tunnel in Avatar: The Last Airbender became a meme.
• Being a popular mystery trope, this happens in many episodes of Scooby-Doo.
• Blue Eye Samurai. Madame Keiji informs Mizu of a passage with a hidden door that leads under the ocean to Fowler's island fortress, which he uses to bring in supplies and Keiji's prostitutes. However this is not an easy shortcut but just the first stage in a Death Course; the tunnel is filled with the skeletons of others who tried sneaking in that way and Mizu nearly drowns when the tunnel floods thanks to a booby-trapped door.
• Work It Out Wombats!: In "Secret Tunnels," the wombats find out that there's a secret underground network of tunnels in the underbelly of the Treeborhood.

Real Life

• Some cities in the US that once hosted large numbers of the Ku Klux Klan will have one or more of these linking common meeting places. The city of Cañon City, Colorado has one linking a old bar's basement and another local business. Needless to say, the shameful origin of the passages often precludes them being tourist attractions.
• There are secret tunnels beneath the Canadian city of Moose Jaw, used to house Chinese immigrants working in the city laundries, as well as rumrunning during prohibition. Though many of said tunnels were actually mundane things like coal storage bins.
• Secret tunnels were built by east Berliners under the Berlin Wall in various escape attempts.
• Extensive networks of tunnels were dug underneath Portland, Oregon and used for highly unsavory activities. (This is a major understatement.) Historical societies have been working to excavate them and to document stories of people who were victims of the human trafficking which they were used for.
• Drug smugglers have dug a number of tunnels underneath the US/Mexican border.
• The tunnels of Củ Chi are an immense network of connecting tunnels located in the Củ Chi District of Ho Chi Minh City (Saigon), Vietnam, and part of a much larger network of tunnels that lies beneath much of the country. They were the location of several military campaigns during The Vietnam War, and were the Viet Cong base of operations for the Tết Offensive in 1968. The tunnels were used as hiding spots during combat, in addition to serving as communication and supply routes, hospitals, food and weapon caches, and living quarters for soldiers.
• Many British mystery works hinge on the presence of a priest hole (hiding places for Catholic priests during times of persecution) in a Big Fancy House to explain how someone got away from a locked room.
• Many important buildings in Washington D.C. (the White House, the US Capitol, etc) all have hidden tunnels underneath them to help evacuate lawmakers and government officials if a crisis jeopardizing their safety occurs.

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