This is a memorial site, not a sightseeing stop. Dress modestly, keep noise down, and do not pose for photographs.
What happened here
Choeung Ek was an orchard and a Chinese cemetery before 1975. Under Democratic Kampuchea it became the place where prisoners from the S-21 security centre in Phnom Penh were taken to be killed. Executions were carried out at night, and the bodies buried in pits across the site.
After the regime fell, excavations in 1980 uncovered the remains of thousands of people from a fraction of the graves identified. Many pits have deliberately been left unexcavated.
It is one of several hundred such sites across Cambodia. It is the best known because of its direct connection to S-21 and its proximity to the capital.
The memorial
A tall Buddhist memorial stupa built in the late 1980s stands at the centre of the site. Its glass sides hold thousands of skulls arranged by age and by the manner of death, and it functions as a place of mourning rather than of display.
The audio guide, included with admission, is exceptional. It is narrated in part by survivors, includes testimony from former guards, and is paced so that you can stop and stand still. Most visitors take an hour and a half.
Fragments of bone and cloth still surface in the paths after heavy rain. The site asks that you do not touch or move them.
Visiting
Choeung Ek is about fifteen kilometres south of the city centre, thirty to forty minutes by tuk-tuk. It is nearly always combined with Tuol Sleng (S-21) in the same morning, and the order matters: S-21 first, then Choeung Ek, follows the path the prisoners took.
Dress respectfully and keep your voice down. This is a working memorial and a place of grief for many Cambodian families, not a tourist attraction in the ordinary sense.
Plan something undemanding for the rest of the day. Most people need it.