The Killing Fields is where thousands of victims of the Khmer Rouge were tortured, killed and buried in mass graves. Skulls of these victims were preserved in an open shelf monument in front of the excavated mass graves.
We rented a couple of bicycles from Mama's Restaurant (Orussey Market) for $1/bike/day. Then we took a 1hr ride to the Killing Fields. We took the eastbound Monireth Blvd, then, about a kilometer after passing a bridge we took the road on the left at a fork in the road (gas station). It's a smooth ride from there on. There's a sign to Cheong Ek Genocidal Center for the final turn off. The entrance fee was $2Usd/p.