Tower of Punishment

To fight Cold sharas, go to the left side, and to fight Hell fire Onyx, go to the right side.

First you need to put the lever down or up in the control room,and then if its the right one,the door will open.

After you fight those two, the door to go to the highest place of tower of punishment will be open.

Best farming area (also leveling up) :
Mouth of Hell-5