The most well known Killing Fields site is at Choeung Ek, about 17km south of Phnom Penh. At this location the Khmer Rouge executed and buried thousands of people in mass graves and there now stands a Buddhist Stupa, a memorial building containing more than 5000 skulls of the victims buried nearby. The glass sides of the building are usually open during the day, enabling a close look at the skulls inside.

After the fall of the Khmer Rouge regime in 1979, more than 8000 bodies were uncovered in the mass graves at Choeung Ek, there are a number of pits dug in the ground and human bones are found all over the site.

Many butterflies and dragonflies fly around the site, perhaps reincarnations of those who died here.