A battle tower.
This is part of the battletowers mod by AtomicStryker.
Battle Towers are towers full of chests and loot, and are heavily guarded by monsters(zombies,spiders,and skeletons). They can spawn anywhere, even at sea as their own island. There is a boss at the very top that gives you access to the final chest at the top of the tower(the 11th floor) if you defeat him. (Although if you are too weak or lazy, it is possible to build up the side of the tower opposite the regular staircase, giving you easy access to the chest). After the boss is defeated, the tower starts blowing up making it more difficult (if not impossible) to access the chests again.
The higher you go up the tower the more blocks can be missing from the floor making it difficult to reach chests and spawners. The chests can hold anything from glass to diamond tools to artifacts, but mob spawners guard the room. There are two spawners per room(but using the strategy mentioned before, you can break open a small hole to break the spawners, and get to the chests easily).
The boss resembles an iron golem, but made out of stone bricks with one eye (painterly pack comes with the install of the Yogbox). The boss shoots ghast fireballs at you, which can destroy the edges of the tower allowing the boss to knock you off very easily but they can be deflected. The boss can jump very high. Be careful if you are using a hit and hide tactic. Sometimes the golem will shoot downward and blow a hole to the floor under making it fall down and if you are hiding there... it might be a problem.
A good way to kill the boss is to stand on a platform away from him and shoot him with a Musket.
Another cool way to kill him is to use the Cloud Boots. They let you jump very high, and match his jumps. You can try and avoid his attacks using them. Using Cloud Boots and maybe a musket (If you're a good shooter!) you can probably beat him.
However, you can avoid this boss by sneaking with the Shift button and then looting the chest.
Each biome has it's own version of the tower. The snow biome one is made out of ice, and when they spawn next to volcanoes they are made out of netherack, watch out though because inside of the netherrack tower, the floors are made of soul sand which is a pain. When thay spawn in the water they will be made out of mossy cobblestone. Even though it is dangerous to assault one there are some methods you can use. One is set it to peacful and simply loot the entire thing with no monsters. Another is to grab everything BUT the top floor so you won't have to fight the golem. The rewards you get for beating a tower are immense including almost every valuable thing in the game and lots of it! Happy Hunting!