A full-fledged city built Beneath The Earth. It's a civilian form of Elaborate Underground Base and comparable to an Underwater City. Typically, these cities come in a few flavors:
- Apocalypse Bunker: A refuge from an apocalyptic threat, thus serving as a Bottle City capable of weathering everything short of planetary crust destruction via Apocalypse How scenario.
- Inhuman Borough: Home to a non-human or once-human race of Mole Men or home to evolved sentient dinosaurs using it as the above mentioned Apocalypse Bunker. While most of the time the residents are natives of Earth, aliens occasionally live in these.
- Buried City: This was once a thriving surface city that has come to ruin, but also been hidden and preserved to an amazing level underground. Usually thanks to an earthquake. If it was highly advanced it may have survivors in the form of a Living Relic, King In The Mountain, Human Popsicle or Perpetual Motion Monster.
Examples:Anime and Manga
- With Earth's surface being uninhabitable due to constant bombardment, humans are forced to live in these at the start of Space Battleship Yamato / Star Blazers.
- In another Leiji Matsumoto anime, Queen Millennia, the aliens infiltrating Earth set up underground cities to survive the coming apocalypse.
- In Action Comics #412◊ Superman discovers the existence of an entire underground city beneath Metropolis.
- Xenoarchaeologists in World of Fire find an underground city under their dig site and decide to break through the still-functioning energy barrier put around it. This stirs up the xenophobic, paranoid security system, which kills them all, then people landing on the world to investigate, then ships flying in orbit overhead...
- In the Matrix movies the only human city in existence, Zion, is hidden underground.
- The Worker's City in Metropolis is a utilitarian and gloomy place underneath the titular city of the movie. It becomes a symbolic of the worker's being an oppressed class, and is a plot point as the film's villains attempt to flood it.
- Atlantis in Atlantis The Lost Empire. Instead of simply being underwater, it was buried beneath the ocean floor, and still inhabited.
- City Of Ember is set in an apocalypse bunker type of city where their supplies and power source are failing.
- The dwarves of Discworld live in vast, underground cities, and living underground is a part of their cultural beliefs. Vimes visits their capital in The Fifth Elephant, which is reached by elevator and holds a vast mine. He's disgruntled to find in Thud! that the dwarves in Ankh-Morpork are starting to build one in the network of buildings that has sunk below ground level.
- The Hyperion Cantos have the high-gravity world Lusus, where all settlements are for some reason underground "Hives" carved into the rock. These are quite extensive; Lusus is a major center of economic and political power in the Hegemony and subsequently (the detective and central character Brawne Lamia's father was a powerful Hegemony Senator).
- The Legend Of Drizzt: Drows live in city-states in the underground domain called the Underdark, after being (supposedly) chased there by the elves. The best known of these cities is Menzoberranzan, the birth home of The Hero, Drizzt Do'Urden. It has 20,000 drow inhabitants plus hundreds of thousands of slaves, grows giant mushrooms and Rothe livestock and trades with other underground humanoid races.
- JRR Tolkien's dwarves often lived in such cities.
- The Hobbit: Before it was conquered by Smaug and turned into his personal treasure horde, Erebor was a dwarven city ruled by the King Under the Mountain.
- Lord Of The Rings: Khazad-dum, aka "the Mines of Moria," was one of the oldest and grandest dwarven cities in existence until its inhabitants Dug Too Deep and awakened an angry and powerful balrog.
- The Silmarillion: Two other dwarven cities, Nogrod and Belegost, existed in the Blue Mountains, and dwarves from them carved out the Thousand Caves of Menegroth which served as the capital of the Elven kingdom of Doriath. All three were sunk beneath the sea at the end of the First Age.
- In Cleopatra 2525 all of humanity live in underground cities because robo terraformers called Baileys roam the surface killing any human they find up there.
- In Falling Skies, starting with Season 2, the remnants of human civilization are living beneath the city of Charleston, North Carolina in an Apocalypse Bunker.
- The Ocampa in Star Trek Voyager lived in an underground city provided by the Caretaker after his species decimated their planet's surface.
- In various Dungeons And Dragons settings, races such as Dwarves, Dark Elves (a.k.a. Drow) and Illithids tend to live in huge underground cities, often including vast open spaces and even farmlands (usually growing some kind of mushroom-based crop).
- Earthdawn. The entire population of the Earth had to hide from an interdimensional invasion. Most of them constructed and found refuge in kaers, magically protected underground cities. The dwarves of Throal actually hollowed out a mountain and used it as their kaer.
- Paranoia takes place almost entirely in Alpha Complex, a massive underground Arcology run by an utterly insane computer.
- Asherons Call had at least two examples. The first was actually called "The Underground City" and it was the former home of Elysa Strathelar and Thorsten Cragstone's rebels. The other was Xarabydun, a settlement in the middle of the desert strangely full of plant life.
- If it survives long enough, a Dwarf Fortress that grows from outpost to Elaborate Underground Base will eventually be a full fledged self-sustaining city able to go without outside trade. That's a big IF though.
- Fallout: The Vaults enabled humanity to survive nuclear war in America but just barely. And they were intended as proof-of-concept models for a Generation Ship that wasn't built in time, hence the various experimental (and often sadistic) situations manufactured.
- In Master Of Orion II the Sakkra are a reptilian civilization with a penchant for underground cities, effectively doubling the population that can inhabit a planet and making orbital bombardment harder.
- Pokemon Colosseum has the Under, a town in the old mines beneath Pyrite Town that at the start of the game is ruled openly by CIPHER. The player frees the town, and by the time of XD: Gale of Darkness everyone has moved to the surface.
- Professor Layton And The Unwound Future has one under the city of London. The inhabitants are made to believe that it is located in the future.
- Former Hell, introduced in Subterranean Animism, the 11th Touhou game. When Hell moved from underground to somewhere else, youkai who were hated because of their powers decided to move to the old location. They formed a contract with the above-ground youkai, where the above-ground youkai are forbidden to go underground, while the underground youkai keep the remaining evil spirits sealed.
- World Of Warcraft: The capital city of the Forsaken undead is the (aptly named) Undercity. It was originally just a series of sewers and catacombs below the palace of Lordaeron, but after the palace was destroyed by Arthas, the undead led by Sylvanas Windrunner claimed it to themselves.
- Ahn'Kahet is an underground city that here and there borders natural subterranean life. It features large, glowy mushrooms, insects of different types and sizes and bioluminiscent birds/bats that fly around. It also contains large number of undead that took over the city as well as the few surviving Nerubians that orginally inhabited the city. While the dungeon itself is fairly linear, players are able get a good view of the massive underground caverns from ledges and combinations of creepy music, darkness and mysterious whispers (courtesy of an Old God under whose range of influence the city is located) make this place quite Nightmare Fuellerific.
- The titular Endtown is the Apocalypse Bunker version crossed over with Inhuman Borough because most of the inhabitants are mutated humans.
- Drow Tales: Similarly to Forgotten Realms (on which the comic was originally based), drows live in underground cities. Most notable of these is Chel'el'Sussoloth, the capital of the drow nation. The city is split across several caverns that are connected by tunnels and bridges, and the ceiling above it resembles a starry night sky.
- Ben 10 Omniverse eventually developed Undertown, an entire city hiding underneath Bellwood's sewers where a great many species of aliens and traders make their living here outside of the watch of humans.
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