The Tuol Sleng Genocide Museum is a museum in Phnom Penh, the capital of Cambodia, chronicling the Cambodian genocide. The site is a former secondary school which was used as Security Prison 21 (S-21) by the Khmer Rouge regime from its rise to power in 1975 to its fall in 1979. From 1976 to 1979, an estimated 20,000 people were imprisoned at Tuol Sleng. Tuol Sleng was just one of at least 150 torture and execution centers established by the Khmer Rouge.