It would be awesome to find big castles with loot, monster spawners, and furniture. You have to search the castle to find the treasure. Maybe the castle could be surrounded by a huge village.
This is a really cool Idea, I would like to see this as well. It would be really amusing to see npcs fighting mobs. There could be both Npc castles and mob castles! the npc ones could have friendly knights you could hire and trade with or something, and the mob castles could be ruins filled with mobs, mobspawners, traps, and loot! (not to say you couldn't loot the npc ones, they just might get mad)
I've never seen a castle, but what I am talking about is huge. The castle should have tons of rooms and everything. I have a very active imagination, so I could have hours of fun with a huge castle.
No nolife has become a king!
Also i like the idea of castles around minecraftia, but how rare?