A former high school converted by the Khmer Rouge into Security Prison 21, where an estimated 20,000 people were imprisoned, tortured, and sent to the Killing Fields of Choeung Ek. Only seven prisoners are known to have survived.
The classrooms-turned-cells remain largely as they were found in 1979 — iron bed frames, shackles, and hundreds of haunting photographs of prisoners taken on arrival. The top floor holds paintings by survivor Vann Nath depicting the horrors he witnessed. It is one of the most difficult places you will ever visit, and one of the most important.
Many of the museum guides are themselves survivors of the Khmer Rouge era. Their firsthand accounts add a dimension that no written panel can match. Allow at least two hours, and consider combining the visit with the Killing Fields of Choeung Ek, about 15 km south of the city.