Tuol Sleng Prison Museum (S-21)

Originally Tuol Svey Prey secondary school in Phnom Penh, this became "Security Office 21" (S-21) or Tuol Sleng Prison which was the biggest prison in Kampuchea. From the 17,000 people imprisoned here between 1975 and 1978, only seven survived. The prison was also used for the execution of prisoners and there are mass graves on the site The museum shows pictures of prisoners, skulls of executed prisoners, documents and information.