Catacombs

Similar to a dungeon, but vastly greater, with a labyrinth like layout, there should be multiple undead mob spawners, as well as a couple rooms with some of the new spawners (the ones that spawn waves of mobs). It should be made out of lots of bricks (tuff or normal) with a little bit of moss, there should be a couple mushrooms here and there, lots of iron grates, lanterns, etc. There should also be a fair few booby traps, like ceilings that come down, corridors and close once you go through, rooms that the can enter, but there is only a secret way to leave, and where they slowly fill with lava. There should also be features rooms, like a room where a ritual of some sort seemed to have taken place, another one with a small water fountain, another that seemed to be someone's private bedroom (with a bed, a lectern with a diary, bookshelves, etc.), rooms full of coffins (chests) maybe, certainly lots of long corridors or varying widths, and trial rooms too. Let me reiterate that I think that if there where lots of redstone circuits it would be interesting, maybe puzzles, but, also lots of deadly one.