Tartarus

Tartarus is the deepest, darkest and most sinister area of the Underworld. It is here where the souls of the wicked and evil are sent and it is also the place where Zeus imprisoned most of the Titans and a giant Cyclops after he ended their reign of destruction.
It is a dark and ominous dungeon-like place located deep beneath the ocean, a few jagged rocks can be seen rising from the sea where Tartarus is and there is also a small island filled with jagged mountains where the Titan Prometheus is imprisoned and each day a giant eagle comes to eat his liver.