Prior to 1975, Toul Sleng was a high school. When the Khmer Rouge came to power it was converted into the S-21 prison and interrogation facility.
Inmates were systematically tortured, sometimes over a period of months, to extract confessions, after which they were executed at the killing fields of Choeung Ek. S-21 processed over 17,000 people, seven of whom survived. The building now serves as a museum, a memorial and a testament to the madness of the Khmer Rouge regime. Much has been left in the state it was when the Khmer Rouge abandoned it in January 1979. The prison kept extensive records, leaving thousands of photos of their victims, many of which are on display. Paintings of torture at the prison by Vann Nath, a survivor of Toul Sleng, are also on display. The museum's famous and controversial “skull map” has recently been dismantled.

(Corner of Street 113 & Street 350 - $2.00 - Open everyday, including holidays, 8AM-5PM Closed for lunch)