Castle Oblivion

Castle Oblivion is an original world first introduced in Kingdom Hearts: Chain of Memories. At the time, it was being used by Organization XIII as a research facility and served as the main setting for the events of the game. In Kingdom Hearts Birth by Sleep, it was revealed that Castle Oblivion was actually a transformed version of The Land of Departure, created by Aqua to protect the world's secrets as well as provide a comatose Ventus with a safe place to rest. In Kingdom Hearts 358/2 Days, it is revealed that Axel was told by Saix to find the chamber where Ventus was sleeping, known as the Chamber of Waking. However, the chamber was never found. Castle Oblivion will reappear in Kingdom Hearts III.