"It seemed a sure bet that by the early '70s we'd be flipping a coin as to whether we'd be spending our holidays on the Moon or at the Poseidon Hilton on the bottom of the Caribbean."Not just Underwater Ruins or an Underwater Base, but an entire city of people living and "breathing" underwater. It's usually created with futuristic technology or powerful magic, and a popular depiction is to have a fully surviving Atlantis with domes and/or water breathing Fish People or Apparently Human Merfolk. Usually though it's a modern attempt at colonizing the ocean floor, or a villain's secret lair. As might be expected, living in such a precarious location makes these cities inordinately prone to having something go Horribly Wrong. Be it sabotage causing the dome to break, an undersea volcano activating, or other disasters. See also City on the Water for cities atop the water instead of underneath. Compare Underground City.
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Anime & Manga
- Daphne in the Brilliant Blue: The main cities of the aquatic New Eden were originally Underwater Cities created to escape the apocalypse. Heroine Maia is the last survivor of one of the cities which was destroyed before it could surface.
- The Fishman Island in One Piece is actually a big mass of land floating in a 2-layer resin bubble, underwater. The light source come from the mystical Sunlight Tree Eve, which transfers sunlight from the surface to the ocean deep.
- Nagi-Asu: A Lull in the Sea has Shioshishio, a small town of Apparently Human Merfolk near a Japanese town on the coast. There's substantial friction between the neighbours over things like fishing rights.
- In Scion, Ethan discovers an underwater city built by an aquatic sub-species of the Lesser Races who were able to escape their lives of slavery.
- Both Marvel Comics and DC Comics have versions of Atlantis, although in both cases Atlantis is a big place with multiple cities.
- There was an arc in Aquaman where half of San Diego slid into the sea following a massive earthquake... and those who survived it instantly adapted to underwater conditions.
- The Elements of Friendship gives us Lyonesse, the capital of Aquastria.
- PokÚdex: The Jellicent are the keepers of one beneath a massive, Jellicent-shaped dome, made out of shipwrecks and flotsam, lit and warmed by underwater vents and populated by sailors kidnapped en masse when their ships pass through the Jellicent's territory. The purpose for this seems to be so that the Jellicent can have access to human technology.
Film — Animated
- The Little Mermaid: Atlantica, and underwater city or kingdom inhabited by mermaids and talking sea life.
Film — Live-Action
- Otoh Gunga, home of the Gungans from the Star Wars prequels, made out of a large number of sealed-off, interconnected domes at the bottom of a large lake.
- The Abyss, in which the NTIs have a very large habitat on the ocean floor. (Whether it's a city or an enormous starship is never really made clear.)
- The Shadow Over Innsmouth by H.P. Lovecraft has Y'ha-nthlei, of the "titanic sunken porticos" and "labyrinths of weedy cyclopean walls." Located off the coast of Massachusetts and home to the Cthulhu-worshipping Deep Ones.
- And don't forget Cthulhu's own sunken city of R'lyeh.
- Isaac Asimov's Lucky Starr and the Oceans of Venus.
- Michael Reaves and Steve Perry's novel Dome, which is set in a futuristic underwater lab complex.
- Underwater colonies are a significant part of the backstory of "The Eve of RUMOKO" by Roger Zelazny.
- A city of cray (lobster-centaurs) is featured in China MiÚville's The Scar.
- In Attack from Atlantis by Lester del Rey, a submarine crew discover an ancient underwater civilization.
- The great city of hi'Leyi'a on the planet Pacifica, in the Star Trek Novel Verse. First mentioned in Star Trek: Titan, it finally appeared in Losing the Peace.
- Handled as realistically as possible in "Ocean on Top" by Hal Clement. A colony of humans is established on the ocean floor, using geothermal power to provide light and a specially-made oxygen-carrying dive fluid in place of air. But since the humans are less dense than water, the humans have to wear weights if they want to stay on the bottom or even have neutral buoyancy. They sleep tied to the ceilings of their buildings.
- Somewhereinitaly in Almost Night. There was also a city called Somewherenotinitaly, but it was destroyed by the Deep Ones.
- The "Undersea" trilogy by Frederik Pohl and Jack Williamson (Undersea Quest, Undersea Fleet & Undersea City) have underwater domed cities protected by Applied Phlebotinum ("Edenite" forcefields). Think of Robert A. Heinlein's Space Cadet done underwater.
- Animorphs has an odd book where the heroes, plus Visser Three, get trapped in a city in an underwater cave. The inhabitants are amphibious mutants whose race is dying, which means that they harvest any humans who sink for DNA.
- They also visit the City of Worms (it's nicer than it sounds) on Leera, an ocean world inhabited by frog-like aliens.
- In Everworld, Poseidon and Neptune both have underwater cities, and they're fighting over Atlantis. We mostly see Neptune's city, where water can be drained, or humans made amphibious, based on the god's whim. (This is not encouraging.)
- In Underneath A Merfolk Tale the merfolk population lives in The City. The merfolk in the story actually live in land and have little dealings with it, although their history and their reasons for leaving it are part of the plot.
Live Action TV
- Stargate Atlantis:
- In the first episode, the city is discovered to be underwater, having been submerged by the Ancients to escape constant orbital bombardment from the Wraith. In a subversion of the Gone Horribly Wrong situation mentioned above, when the shield fails, the city surfaces.
- In a Double Subversion, It didn't happen the first time around: In an alternate timeline, the city was flooded, and Dr. Weir escaped drowning in a time-traveling ship; she then convinced Ancient scientist Janus to add the fail-safe.
- ORCA in Ocean Girl is halfway between this and Underwater Base. The ORCA City project may be closer to this trope.
- seaQuest DSV is set in a world where the ocean floor has been so heavily colonized that there are whole underwater nations.
- In the cartoon segments of The Aquabats! Super Show!, the band tries infiltrate an underwater city beneath the moon's surface to save Jimmy the Robot.
- In Star Trek: The Next Generation, still reeling from his recent assimilation by the Borg, Picard is briefly tempted in "Family" to quit Starfleet and join the Atlantis Project, who are aiming to build one of these on the floor of the Atlantic Ocean.
- Several Dungeons & Dragons settings include undersea civilizations of merfolk, tritons, sahuagin or the like; some of these use air-filled domes as housing for surface-dwelling visitors. The Known World/Mystara campaign setting has the Kingdom of Aquas, which was once part of the Empire of Alphatia.
- In New Horizon, Aquilon's Reach has multiple underwater cities, as well as some atop glaciers. Unsurprisingly, they also boast the best navy in game.
- See the Shadowrun, 2nd Edition supplement Portfolio of a Dragon: Dunkelzhan's Secrets; in his will Dunkelzhan left a bequest of 5 million nuyen to the first party to establish a self-sustaining community of at least 100 persons on the ocean floor. Yamatetsu Corporation eventually won the bequest with their SoaTome AquaDomes.
- Transhuman Space has Elandra, an Australian-founded "free city" under the Pacific. It's more of a town than a city, really, but a respectably-sized one.
- Underwater cities have cropped up occasionally in the lore of Warhammer 40,000.
- Rapture from BioShock is a Diesel Punk and Bio Punk city that's completely underwater, save for a lighthouse that contains a bathysphere to bring people down from the surface.
- The Call To Power series has sea cities.
- Aquaria has Mithalas City, which has long since been completely ruined after a Path of Inspiration corrupted its patron deity into a horrible monster. Guess what you end up fighting in the ruined cathedral.
- In Mass Effect, it's mentioned that Kahje, the homeworld of the aquatic hanar has 90% of the surface covered by water and features impressive domed cities, which they originally built for the drell after the hanar rescued most of the species from their dying homeworld, two centuries previously.
- The main premise of Atlantis Underwater Tycoon is to build and maintain one.
- A new feature in the Rising Tide expansion for Civilization: Beyond Earth is the ability to build cities on ocean tiles.
- The Hylotl from Starbound live in these. And it looks awesome.
- ANNO 2070 has underwater cities...except they aren't actually cities. Rather, they're underwater plateaus (implied in-game to be parts of our world submerged by climate change) which all three major factions can build farms and factories on. These largely-automated facilities provide supplies which are rare or nonexistent abovewater, making them a key part of the middle and late-game. The game's lesser faction, the S.A.A.T. (Scientific Academy for Advanced Technologies) specialises in building and working with such settlements, an attribute which was further developed in the game's expansion, The Deep Sea.
- Sunless Sea: There are several populated cities beneath the Unterzee that you can visit once you get the Zubmariner expansion. Most have their own unique peculiarities — Hideaway is built on the shell of a colossal hermit crab, Dahut is populated by Drownies and has water that can be breathed like air, Wrack is built out of sunken ships and home to wreckers, Nook is tucked into the maw of... something huge and lamprey-like, and Anthe is built into a crystal formation and home to people who seek to become more crystalline themselves.
- Almost the entire world of Aquapunk. With Fish People and everything.
- In Question Duck, one character claims to have been to an underwater city home to fish and dolphin people and to mermaids, which he helped defend against evil seals.
- Zukahnaut's protagonist finds himself first imprisoned in, then ruling over, an undersea kingdom in a story where he swaps bodies with its leader.
- In The Gamer's Alliance, Adlivun is a thriving underwater city populated by merfolk known as merrows.
- Futurama featured the Lost City of Atlanta — a joke on Atlantis, of course — which was turned into a City on the Water to attract more tourism, but became overloaded with buildings and construction and sank. The citizens who stayed behind ended up evolving into mermaids and mermen by the 3000's, thanks to the caffeine from the Coca-Cola plant (somehow) speeding up their evolution.
- Sealab 2020 opening credits.
This is the year two thousand and twenty. The place is the Challenger seamount, the top of an underwater mountain, a complex beneath the sea. 250 men, women and children live here, each of them a scientist-pioneer. For this is our last frontier, a hostile environment which may hold the key to tomorrow. Each day these oceanauts meet new challenges, as they build their city beneath the sea. This is Sealab 2020.
- Sealab 2021
- ... not to mention the other Sealab featured on Centurions .
- They visited Atlantis on The Fairly OddParents!. Also, Clevelantis.
- King had Bubble Town, the capital of the nation of Undersea, ruled over by the despotic Cousin Tess.
- The Adventures of Super Mario Bros. 3 had one in the episode "The Ugly Mermaid". It was a bizarre case in that the city had domes with air in them, despite the merfolks not being able to breathe air.
- Samurai Jack: The episode "Jack Under the Sea" features the underwater city of Oceanus, home of an amphibious alien tribe called the Triseraquins, built as a system of waterproof domes on top of high-tech towers. It used to be a City on the Water instead, but Aku banished it beneath the ocean to where it is now. It returns to the surface by the end of the episode.