Tuol Sleng Genocidal Museum is the former Tuol Sleng High School.
In 1975, during the Khmer Rouge regime, the school was used as a prison and torture center, know at the time as S -21.
Thousands of Cambodian and number of foreigners were housed and tortured there until they were executed.
Today the site is a museum, where visitors can walk among some of the cells and look at the photos of hundreds of people who died there.
There are also paintings, painted by artist Vann Vath, a former prisoner, that depict the torture of prisoners.