Add "Creepy Castles"

Basically, they are castles that can be found in most biomes which have a lot of valuable loot inside. However it's guarded by hostile mobs like the creeper, zombie, skeleton and witches. I think this is a good idea because there's room for so much more features such as adding a custom mob specifically for this structure which makes it more unique and special rather than just another random structure with the same basic mobs.

Hope you take this into consideration!