Would actually make for an interesting update to the Plains biome.

Black Forest == Burial Chambers & Troll Caves
Swamp == Sunken Crypts
Mountains == getting Mountain Caves soon
Plains == flat, rocky sadness

I assume Mistlands will also have a sort of dungeon when it releases, or shortly after; along with the other biomes.

So something like "Abandoned Mines" would be neat! Would also give us access to much more gold coinage, or gold ore, assuming it could be used for things. Might also be a good time to toss in the update to the Trader as well. ;)