In 1975 this regular suburban high school was taken over by Pol Pot's security apparatus and turned into the country's largest prison/detention centre/place of torture - the infamous S-21. Between 1975 and 1978 only 7 of 17,000 prisoners are known to have survived incarceration here.

Now it is at once a monument to the barbarity of the Khmer Rouge, yet still little more than an ordinary suburban high school. The Khmer Rouge were quite meticulous in cataloging their efforts; including photographing all of the detainees. As a keen photographer it is hard to imagine what was going through the minds of the prison photographers as they captured what they must have known would be the last images of these (such ordinary looking) Cambodians.

Possibly most chilling of all are the 14 cells in which the liberating Vietnamese forces that swept into Phnom Penh in 1979 found freshly tortured victims of the KR. Each cell has a photograph on the wall of the scene that greeted the invading troops, plus the entire contents of the cell; just as they found them.

I first visited this museum in 1993, and my latest visit was just as moving.