Devar-Toi

Devar-Toi is a fictional minimum-security prison located in Thunderclap, an area of End-World in the Dark Tower series. Several of the events of the novel The Dark Tower occur here. A campus-like complex, Devar-Toi is also known by the names Algul Siento and Blue Heaven. The guards of Devar-Toi are a mix of can-toi, humes and taheen, with the management staff consisting primarily of taheen. The Devar-Toi is wardened by Pimli Prentiss (a human) and Finli O'Tego (a taheen). The complex houses numerous Breakers, psychics of various types employed by The Crimson King, using their powers to attack and destroy the Beams that support the Dark Tower.

Though the surrounding landscape's light quality is always dim due to a perpetual cloud-cover, Devar-Toi itself is lit by a man-made lighting device left by the Old Ones, creating a sharp contrast in mood and coloration between the prison and the outside land.

Devar-Toi and its operations are shut down permanently by Roland Deschain, Eddie Dean, Jake Chambers, and Susannah Dean.