Tartarus

In classic Greek mythology, below Heaven, Earth, and Pontus is Tartarus, or Tartaros (Greek Τάρταρος, deep place). It is either a deep, gloomy place, a pit or abyss used as a dungeon of torment and suffering that resides within Hades or the entire underworld with Hades being the hellish component. In the Gorgias, Plato (c. 400 BC) wrote that souls were judged after death and those who received punishment were sent to Tartarus. As a place of punishment, it can be considered a hell. The classic Hades, on the other hand, is more similar to Old Testament sheol.
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Noun
1. a place where the wicked are punished after death
(synonym) Gehenna
(hypernym) Hell, perdition, Inferno, infernal region, nether region, the pit

(n.)
The infernal regions, described in the Iliad as situated as far below Hades as heaven is above the earth, and by later writers as the place of punishment for the spirits of the wicked. By the later poets, also, the name is often used synonymously with Hades, or the Lower World in general.
  

[Greek] 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, Earth, and Eros, it is one of the first entities to exist in the universe. While Hades 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 gods; the Titans were condemned to Tartarus after losing their battle against the Olympian gods, and the hecatoncheires stood over them as guards at the bronze gates. When Zeus overcomes the monster Typhus, born from Tartarus and Gaia, he hurls it too into the same abyss. However, in later myths Tartarus becomes a plac...
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Tartarus, Tartaros (Greek) Son of Aether and Gaia (earth), who by his mother became father of the giants Typhoeus and Echidna. Other names for Tartarus as a deity are Pluto, Hades, Orcus, and Dis -- all referring to the underworld. As a place, in the Iliad it was one of the four regions, as far below Hades as heaven or Olympus is above earth, and into which were thrust the titans who rebelled against Olympus. In later times it became synonymous with Hades. In theosophical literature it is sometimes equated with avichi.
With the first appearance of Lemuria, the three polar giants were imprisoned by Kronos in the polar circle, where they were kept in by seas; but they were liberated by Zeus in order to overthrow Kronos, which points to the supersession of Lemuria by Atlantis.