Ruins is a mod that spawns Structures in your Minecraft worlds upon generation, similar to Villages or Strongholds. Every Structure is defines by a template and configured to spawn under specific conditions, and all of that can be changed by you!
There is a lot of Structures already included, and there's bound to be more added.
For more info go to the forum of minecraft: http://www.minecraftforum.net/topic/1113099-
Required Stuff to have installed beforehand: