What about the underground biome, or the civilization or built up biome?
Civ
-Castle
-Village/Town/City with walls or open
-Tower with many z axes up
Underground
-Tunnel and Room Dungeon
-Caverns
-Tunnels
-Rooms
-Hell w/lava and such
-Jungle with lost world dinosaurs and such
City and Underground biomes would have to adopt some of the characteristics of the surrounding biome, like an underground jungle will have jungle or whatever and generally be shaped like caverns, etc...
Not sure exactly how you are doing it and what counts as what, but there should be underground and built up areas, right?