S-21, also known as the Tuol Sleng Genocide Museum, was a former high school in Phnom Penh, Cambodia, that was converted into a prison and torture center during the Khmer Rouge regime from 1975 to 1979. It is estimated that around 14,000 people were imprisoned there, with only a handful surviving. The facility was used for interrogation, torture, and execution. Today, S-21 serves as a museum to educate visitors about the atrocities committed during the Cambodian genocide. It houses photographs, documents, and personal stories of the victims, aiming to preserve the memory of those who suffered and to promote awareness of human rights violations.