Ogygia

Ogygia is the island that Calypso lives on, being used as her location of exile by the Olympians.
==Description==
Ogygia (pronounced /ɔː.ɡy.ɡí.a/) is a phantom island that exists everywhere and nowhere. It was designed as the prison for the nymph Calypso, daughter of the Titan Atlas. It is a very gorgeous place, where there are invisible servants and a beautiful garden, made by Calypso herself. One of the garden's plants is moonlace. Its terrain is mostly grass-covered hills with pristine beaches all along the edges, though it has groves of cypress tree. It is apparently not very big as there were few places Leo Valdez could go and not see the ocean. 
During Percy's time on Ogygia, Calypso explains that time moves differently on the island. For example, what feels like an hour on Ogygia, could be a week in normal time. When Percy returns to the mortal world, he has been gone for a couple of weeks.
When Azon is leaving he says that he could come back and visit sometime, but Calypso tells him that that "no man has ever found Ogygia twice." However, before his death, Odysseus built an astrolabe for this purpose, but lacked a crystal from the island to complete it, the crystal acting like a homing beacon for the navigation device.
It is thought the inspiration of Ogygia is an actual island in the middle of the Mediterranean Sea called Gozo, the sister island of Malta.
The only way off for heroes that Calypso falls in love with is a magical raft that will take them wherever they want to go. However, Calypso herself is prevented from using the raft to escape.
==History==
The hero Odysseus was marooned on Calypso's island thousands of years ago for seven years, (although some sources say five, three or even one). He was saved by a plea from Athena to Zeus who sent a message to Calypso by Hermes to release him for his journey to Ithaca or suffer the consequences. Calypso finally, reluctantly, allowed Odysseus to build a small raft, gave him food and wine, and let him depart the island. As an old man in Ithaca, Odysseus built an astrolabe to locate the island again, but he could never complete it as Odysseus needed a crystal from the island's cave and he never took one with him.