Tartarus

Tartarus are the mysterious locations appears in Monster Girl Quest: Paradox.

In the Paradox trilogy universe, thirty years prior to the game's events, a catastrophe known as the Great Disaster drastically altered the entire world within a day. As a result, seven huge black holes called Tartarus appeared all over the world; each Tartarus had huge dungeons within, filled with Apoptosis, and lots of highly advanced relics and technologies called Machina, or Machines, were discovered.