Jedi containment vault

A vault built by the Rakata species was located in the the Tomb, an ancient prison on the planet Belsavis, and was used by the Jedi Order to contain Jedi who had lost their minds and fallen to the dark side of the Force after encountering the entity known as Sel-Makor on the planet Voss. Located in the Warlord's Deep region of the Tomb, the vault was guarded by the Jedi Master Averon, who remained alone in the vault to tend to his fallen friends. However, during the invasion of Belsavis, Imperial forces invaded the vault on the orders of Lord Atren and slew Averon, freeing the insane Jedi.

Text and facts from the “Jedi containment vault” article on Wookieepedia, licensed under CC BY-SA 3.0. Modified for this site.