Minecraft wiki entry for Defeating_a_dungeon, associated text: The spawner in the center of the room is the key prize. You can destroy it if you like (it gives a modest amount of experience when broken with a pickaxe) but that is strongly discouraged unless you never, ever, ever want to farm the spawner. Once you're done, look in the chests. The loot normally contains a lot of things, but the best prizes are golden apples, horse armor, name tags, enchanted books, and saddles.