

Xenoarchaeologists in Star Wars (Marvel 1977)'s "World of Fire" find an underground city under their dig site and decide to break through the still-functioning energy barrier put around it.In Action Comics #412 ◊ Superman discovers the existence of an entire underground city beneath Metropolis.The Marvel Universe has several subterranean civilizations, including The Mole Men, The Lava Men, The Deviants and even a sunken Atlantean city whose inhabitants age instantly when exposed to the surface's atmosphere for some reason.There's an enormous, spiral shaped Genius Loci buried under Kurozu-cho that appears to be the source of the town's "curse". Uzumaki features an example that seems to fall into type three, although its origins are cloaked in impenetrable darkness.The city of Lux in Texhnolyze is somewhere in between type 1 and 2.Anyone who dares to reach the surface is soon hunted down by Humongous Mecha-driving Beastmen.
HUMANKIND CITY CAP SERIES


A small part of it, Iruburu, is still inhabited by former delvers who relinquished their humanity to the Abyss or became trapped by the city. Nobody knows how an entire city ended up down there, but the few reports that have made it to the surface describe it as a City of Gold. Made in Abyss: The Capital of the Unreturned in the sixth layer.It was originally an underground shipyard where the Bakufu built its ships, but Yoshiwara and its residents were moved down there after its original destruction during the Joi war. Yoshiwara in Gintama is an underground Red Light District with its own laws separate from the Bakufu.In Dragon Ball Z: Bojack Unbound, the final arena where Bojack is fought is an expansive Victorian-era city built underneath the island where the tournament takes place.After it was rediscovered, when people realized the place was filled with abandoned treasure (even the walls were plated with gold), not to mention the prophecy that the one who defeated the Mad Sorcerer would inherit the whole kingdom, it set off a Dungeon Crawling craze.

One thousand years ago, a Mad Sorcerer sank the whole thing into the ground without a trace as part of a successful and misguided spell to make the inhabitants immortal after the sudden death of its king traumatized him. The titular dungeon in Delicious in Dungeon was once the castle and surrounding town of the Golden Kingdom, a prosperous human civilization.United Earth Headquarters in Aldnoah.Zero is pretty big: it has enough living space to house thousands of refugees, and when the Vers Empire invades in Episode 11, their attack helicopters and sky carriers are able to fly around the base at high speed with plenty of room to spare.
