When you mention Cambodia to people, one of the first things to come up is the Khmer Rouge and the genocide that happened in the country. Phnom Penh is host to two of the most famous of these genocidal artifacts: the Killing Fields of Choeung Ek and the school turned torturous prison called Tuol Sleng (also known as S-21). To visit is to step into a disturbing past.

We started our day with a trip to Choeung Ek. A relatively small plot of land on the outskirts of Phnom Penh, it is plain in appearance and our tuk tuk driver missed it entirely on the first pass. While outside appearances are unassuming, this small plot of land was the site of almost 9,000 executions carried out under the Khmer Rouge regime. Typically taken from Tuol Sleng, they were trucked here to be executed on arrival. Since bullets were expensive, most executions were carried out with simple tools like rakes, hoes, shovels, and machetes. On occasion, palm stems were used to slit throats. To mask the sounds of murder, loud music was played 24 hours a day, and strong chemicals were used to hide the smell of decay.

Walking around the site, there are many pits in the ground marking the sites of mass graves. Bone fragments, teeth, and articles of clothing lay about the grounds, exposed by rain. Periodically, these are collected and cataloged. It’s hard to comprehend the magnitude until you visit the memorial stupa where they have arranged some 5,000 human skulls in layer after layer, sorted by age, gender and ethnicity. Then the staggering scale of the genocide becomes sobering.

We left Choeung Ek and returned to the city to rest and eat before continuing our tour at Tuol Sleng. Tuol Sleng was, of all things, a school before it was pressed into service as a prison. After the fall of the Khmer Rouge, the buildings were left as they were. Rooms are empty except for the beds prisoners were chained to. There are still marks of blood on the floor where beatings took place. In one building, rooms were converted to prison cells. Each cell was just large enough to lay down. Dark and breathless, it’s hard to imagine the suffering that took place here during the summer heat. Many never left S-21 and most of those that did left for Choeung Ek.