The audio guide (French available) is included in the ticket. Expect to pay 6 USD, spend 1.5 to 2.5 hours on-site, and take 30 to 40 minutes by tuk-tuk from the center (negotiate the round trip with waiting time).
Respect the marked paths: the ground still holds human remains. Avoid smiling group photos — this is a place of memory for Cambodian families as well as visitors.
To combine S-21 and Choeung Ek in the same day: