All underground Neighborhoods are part of the Underground District, rather than the District above the Neighborhood.
Unlike normal Districts, each underground neighborhood has a separate spawn category.
- Old Stilwater - controlled by Bums
- Stilwater Caverns - controlled by Ultor, populated by Bums
- Rounds Square Shopping Center - controlled by Ultor
- The Pyramid - controlled by Ultor
- Although located underground, the casino under the Marshall Winslow Recreation Center is part of the New Hennequet neighborhood, and is not part of the Underground district.
- The District name is never given in-game.