In 1975, used to be Toul Sleng is a high school that became a detention and interrogation centre when the Khmer Rouge took over.  It became Security Prison 21 or S-21 where thousands of innocent Cambodian people, and several foreigners were tortured and killed.  Maybe not for the weak-hearted, a visit to Toul Sleng Genocide Museum is intensely a depressing experience. The school’s former classrooms were converted into tiny prison and torture chamber. Prisoners were photographed and forced to give an account of their autobiographies from childhood until they were arrested. The rooms display harrowing black and white pictures of its prisoners, some of which were taken after they were tortured.  Many will cringe as they learn the methods by which the prisoners were gruelingly tortured to death.