Security Prison 21 (S-21), Phnom Penh, Cambodia: This former torture and execution centre is now the Tuol Sleng Genocide Museum, dedicated to the victims of the Khmer Rouge. The torture rooms have been left as they were found and, as the Khmer Rouge thoroughly documented their actions, there are many photos on display of the estimated 20000 victims. Sobering.
The buildings at Tuol Sleng are preserved as they were left when the Khmer Rouge were driven out in 1979. The regime kept extensive records, including thousands of photographs. Several rooms of the museum are now lined, floor to ceiling, with black and white photographs of some of the estimated 17,000 prisoners who passed through the prison.

The site has four main buildings, known as Building A, B, C, and D. Building A holds the large cells in which the bodies of the last victims were discovered. Building B holds galleries of photographs. Building C holds the rooms sub-divided into small cells for prisoners. Building D holds other memorabilia including instruments of torture.

Other rooms contain only a rusting iron bedframe, beneath a black and white photograph showing the room as it was found by the Vietnamese. In each photograph, the mutilated body of a prisoner is chained to the bed, killed by his fleeing captors only hours before the prison was captured. Other rooms preserve leg-irons and instruments of torture. They are accompanied by paintings by former inmate Vann Nath showing people being tortured, which were added by the post-Khmer Rouge regime installed by the Vietnamese in 1979.

Today, the museum is open to the public, and along with the Choeung Ek Memorial (The Killing Fields), is included as a point of interest for those visiting Cambodia. Tuol Sleng also remains an important educational site as well as memorial for Cambodians. Since 2010, the ECCC brings Cambodians on a 'study tour' to the Tuol Sleng, Choeung Ek and finishing at the ECCC complex. During 2010, around 27,000 Cambodians visited the museum through this tour. (See ECCC Court Report January 2011) Some believed that ghosts of the victims continue to haunt the place.[20]

A number of images from Tuol Sleng are featured in the 1992 Ron Fricke film Baraka.
https://www.jacobinmag.com/2015/04/khmer-rouge-cambodian-genocide-united-states/