Melione's Cave is an entrance/exit in the Underworld that leads to the mortal world. The cave is used by Melione the goddess of ghosts. To get to the cave one has to not only cross the river Lethe but climb a steep cliff. The only mention of the cave is in The Sword of Hades. After the when Ethan Nakamura entered Hades raided it taking The Sword of Hades. After stealing the sword Ethan searched for a safe way out and was told by Sisyphus to talk to Melione. Ethan apparently made some sort of bargain with her in which she allowed he and Iapetus (whom Ethan had since raised from Tartarus) to escape. In the end Ethan does use the cave but by that time he had lost the sword and Iapetus whom he was sent to raise had no memory.