Sanitarium

The Sanitarium was the only structure maintained on the surface of Nathema in the centuries after the Ritual of Nathema destroyed all life on the planet. The Sith Emperor Vitiate continued to use the Sanitarium for his own purposes during the following centuries, building a secure vault that kept some of his most-guarded secrets. He experimented with training Force-users to survive the void in the Force, resulting in Nathema Zealots, who became guards of the Sanitarium, while day-to-day affairs were being taken care of by specially trained Abyssin Keepers. The powerful Force-users who opposed Vitiate were sent to the Sanitarium to be experimented upon, unable to access the Force to resist or escape. Eventually, Vitiate sent his daughter Vaylin to the Sanitarium to subject her to mental conditioning; she became the only inmate to ever leave the Sanitarium alive.

Years later, Vaylin assumed her father's Eternal Throne and became aware of her mental conditioning, ordering Jarak, the scientist responsible for it, to find a way to undo it. After Jarak had a breakthrough, he invited Vaylin to return to Nathema and subjected her to a ritual of his design. However, it did not go as intended and Vaylin's power raced out of control, killing everyone in its path. She eventually found the will to break her bonds and left the surface of Nathema, after which she used the Force to remotely trigger the destruction of the Sanitarium.

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