From 1975 to 1979, Cambodia, one of the most brilliant civilizations appearing on earth, must undergo a dark period of destruction from Khmer Rouge. Tuol Sleng Genocide Museum, Phnom Penh is a strong evidence of the history about terrible massacre nearly 40 years ago in Cambodia.

Initially, it was Tuol Svay Prey High School before the buildings was destroyed and remodeled into Security Prison 21 (S-21) with durable windows in iron and barbed wire around. All classrooms were used in a new role: the jails, interrogation room and torture chambers. In the period of 4 years under the Kmer Rouge reign, this prison confined about 17,000 people (other sources said that figure was 20,000), mostly members and previous soldiers of Kmer Red convicted of betrayal or government officials, the intelligentsia because they were suspected of being spies or dangerous forces for government. Even their families, including the elderly, women, and children were arrested, interrogated and brutally executed at the Choeung Ek extermination center, and then their corpses were buried in mass graves inside the prison grounds.

Pictures illustrating many cruel forms of torture and homicide along with records of prisoners have been kept in the museum, whose role is the powerful voice denouncing the crimes of the Khmer Rouge government in the large-scale genocide in Cambodia. The interrogation room and torture chambers make a sense of horror and bleak with blood on the walls, skulls in wooden cabinets and rusty torture instruments with detailed explanations about the way to use them. Previously, a map of Cambodia made ​​from 300 skulls of underprivileged victims was once displayed in here as a most tragic image, but was subsequently removed in 2002 because it is controversial as an insult to the dead.

More than three decades have elapsed since the first time the world knew the tyrannous genocide of Khmer Rouge government in Cambodia. With pictures, artifacts and documents, the current museum attracts a large number of visitors from all over the world. However, not everyone is brave enough to witness this historical tragedy without feeling fearful.