The Tuol Sleng Genocide Museum is a museum in Phnom Penh, the capital of Cambodia, chronicling the Cambodian genocide. The site is a former high school which was used as the notorious Security Prison 21 (S-21) by the Khmer Rouge regime from its rise to power in 1975 to its fall in 1979. Tuol Sleng (Khmer ) means "Hill of the Poisonous Trees" or "Strychnine Hill". Tuol Sleng was only one of at least 150 execution centers in the country, and as many as 20,000 prisoners there were later killed.