Castles

Every Biome has a castle big or small with chests in vaults where you must crack the code using things in other rooms. It could be abandoned or full of NPCs. There could be villagers in armour that fight approaching enemies, Royal Dogs, Golden Golem that is like the royal guard, King and Queen Villagers that wear robes.

If this was a future update maybe there could even be a nether castle with Netherite golems around the fortress attacking trespassers (Anyone from the over world)