Location from Attack on Titan by Hajime Isayama
A lightless slum beneath Wall Sina where Levi Ackerman grew up. Crime, poverty, and people the surface world pretends don't exist.
Beneath the polished streets of Wall Sina lies its conscience — or its lack of one. The Underground City is a network of caverns and tunnels where the dispossessed live in permanent twilight, breathing recycled air and fighting over scraps the surface discards. No sunlight reaches here. The economy runs on theft, black markets, and the occasional merchant willing to trade with people who technically don't exist in any census. Children grow up learning to use knives before they learn to read. Levi Ackerman survived this place, which tells you everything about his lethality and nothing about his capacity for trust. The Military Police technically has jurisdiction down here but rarely bothers — the Underground is self-policing in the way that all places abandoned by authority become self-policing. Violently.
Also known as: the Underground, beneath Sina, the caverns