This is Toul Sleng, or S 21, before 1975 a high school in Phnom Penh. It became a detention and interrogation center during the Pol Pot regime. Here over 12,000 people, not including children were imprisoned, tortured and eventually murdered. Only seven detainees are known to have survived.

In one class-torture-room the blood has soaked into the tiles as you can see.
Here are pictures of some of the children detained here.

The city and the prison were liberated 7 January 1979. As the Vietnamese army entered the city, the maniacs at Tuol Sleng murdered the last fourteen of their prisoners. They were buried on the school grounds themselves since their bodies were discovered as they lay in the buildings, still warm but dead.

The Khmer language motto posted reads, "That we may remember and never allow this to happen again."