This castle is a structure generated by the Better Dungeons mod. It first appears as an incomplete 1x1 pillar of endstone with ladders climbing one face. The castle at the top of the pillar is a large structure made of end stone. In the middle, ladders lead up to higher layers with loot and monsters.This castle is guarded by skeletons or walkers and there is a Necromancer Boss within.
With diamond scale armor (full) and a diamond giant sword, to sometimes block damage, this dungeon can be relatively easy.
A bow to deal with creepers is recommended.
Another good way to deal with creepers without arrows is a poison staff. Simply right click the creeper with it (probably from any distance) and it will be poisoned. This will take it down to 1 health, so long as you try to avoid it. Then, simply hit it once. Uses almost no durability, and very effective.
It is recommended to have 25 food points worth of food to restore. be SURE to deal with creepers first, you don't want holes all over with a chance to fall through.
Lets start with some pictures.
This is the Tower from the Ground: as you can see, it is pretty high up, and shows up well on the mini-map.
Climbing the Ender Stone ladder, near the top of the big Ball
there are blocks leading up, sorta like stairs. just check for loot, jump up to the next level, and kill all THOSE monsters. (beware, they can spawn behind you). Then, kill everyone in that level, and proceed to the next one.
After killing creepers and anyone near, go to towers on LEFT and RIGHT.
At the top are the final loot chests.
These are the last chests, after this go back down and watch your step.