The Netherworld
From Gekkeiju Online
The Netherworld is the land of the dead, controlled by the fearsome Lich Queen, Shakir. The Netherworld is far from the paradise that the Gods promise to their followers. The Netherworld isn't populated by those in the favor of their Gods but by the corrupted ones who have been turned into undead by the Lich Queen.
Some ancient texts speak of a ritual that could open portals to The Netherworld and allow traveling.
