A Vulcan retreat for the rehabilitation of criminals where T'Pring works, and whose inmate Xaverius the pirate Angel tried to free in The Serene Squall.
The Ankeshtan K'til Retreat is a Vulcan institution that seeks to reform offenders through logic. Spock's betrothed T'Pring serves there, and her work is one reason the couple see each other so rarely. It features in the Strange New Worlds episode The Serene Squall.
Most of its inmates are V'tosh ka'tur, Vulcans who have rejected pure logic. One of them, Xaverius, is the partner of Angel, the pirate captain who boards the Enterprise in the guise of an aid worker. Angel takes the ship and offers Spock's life to T'Pring in exchange for the prisoner.
Spock ends the stand-off by staging an affair with Nurse Chapel in front of T'Pring, which frees her of any duty to bargain. Afterwards he reflects that Xaverius is an assumed name and that the prisoner may be his half-brother Sybok.