Chambers of Repose and Waking

The Room of Sleep was a room in Hollow Bastion built by the apprentices of Ansem the Wise. After the apprentices banished Ansem and became Nobodies, Xemnas would travel to the room. In the scene in Kingdom Hearts II: Final Mix+, Xemnas entered Ansem's computer room, entered a data disk into the machine, and entered the password "Another", after which he entered six more passwords.

This caused a passage to appear below the lab, which had a long path spiraling down to a long hall with doors locked with electronic locks and bound with chains. At the end of the hall was a door. Inside was a single throne which Xemnas would sit on, as well as the armor of a Keyblade warrior named Aqua, including the Keyblade. Xemnas would speak to the armor, addressing it as a "friend".

Apparently, Xigbar often eavesdropped on the conversations, and told Zexion that he heard another voice once. He also told Zexion he suspected that there was a link between the Room of Sleep and Castle Oblivion, where, allegedly, the "Room of Awakening" is.