Tartarus

Tartarus are the pits which appear in Monster Girl Quest: Paradox. In the Paradox Trilogy universe, thirty years before the game's events, a catastrophe which is known as the Great Disaster drastically altered the entire world within the same day. As a result, seven huge black holes called Tartarus appeared all over the world; each Tartarus had massive dungeons within, filled with Apoptosis, and lots of highly advanced relics and technologies called Machina, or Machines, were discovered.

As evidenced by the destruction of Heaven, the Tartarus literally tear through the fabric of reality itself. It's not just like a massive explosion created them. A piece of something from another world tore through into this one and built the pits which the inhabitants of the Paradox world refer to as Tartarus. It is connected to Chaos.

Known Tartarus lists

 * Ilias Cont. South Tartarus
 * Ilias Cont. East Tartarus
 * Sabasa Cont. North Tartarus

Trivia

 * Tartarus, the Greek underworld, is based off Greek mythology. Tartarus was two things. It was the Greek underworld, and also a primordial force, the ancestor of the Titans. While Hades was the place of the dead, Tartarus was the place where the worst of the worst went, such as the Titans. Think of it like Hell, the opposite of Heaven. Tartarus being deeper than Hades itself would connect to the fact Tartarus is the deepest location accessible in the Paradox world. There were five other primordials, but whether they will be mentioned in Paradox cannot be said.