Tartarus

Tartarus, in mythology, is the darkest and deepest area of Hades' realm, known as the Underworld, where the gods imprison their enemies, chiefly the Titans. Tartarus is also the primordial god of Nothingness, son of Chaos. Kronos is known for being held there. When a monster is slain, it is sent to Tartarus until they reform, for a time ranging from weeks to centuries.

Tartarus is the lowest region of the world, as far below earth as earth is from heaven. According to the Greek poet Hesiod, a bronze anvil falling from heaven would take nine days and nights to reach earth, and an object would take the same amount of time to fall from earth into Tartarus. Tartarus is described as a dank, gloomy pit, surrounded by a wall of bronze, and beyond that a three-fold layer of night. Along with Chaos, Gaia, and Nyx, it is one of the first entities to exist in the universe.

While Erebus is the main realm of the dead in Greek mythology, Tartarus also contains a number of characters. In early stories, it is primarily the prison for defeated enemies. The Titans were condemned to Tartarus after their battle with the Olympians, and the Hekatonkheires along with the Cyclops and Gigantes, were imprisoned there before that. The Hekatonkheires, after the Titanomachy (Titan-War), became the guards of Tartarus with the Titans imprisoned there.