For anyone thinking of taking a moto / tuk tuk to the Killing Fields, don't do it. I'm not trying to put the poor bastards out of business, but a recent trip there was the bumpiest, most crazy ride and although the road doesn't look that bad, I don't recommend it.
We were hanging on, trying to stop our teeth from slamming together and to keep our bums on the seat. Those little motos are quite well-made but we were shaking about like dice in a can. Terrible road. Although it only goes on for 20 minutes or so, we watched with jealousy as people cruised past on mororbikes. I would recommend taking a motorbike, even if there are 2 of you.
Also, take a Kroma - one of those scarfs the Cambodians wear. Throughout my trip it was one of the best purchases I made - perfect for protecting yourself from wind, rain, pollution, dust and dirt, especially good for dusty roads around Cambodia.
The Killing Fields are not far away from Phnom Penh, since they are the mass burial ground for many of the political opponents of the Khmer Rouge regime, along victims of internal purges. Men, women and children were brought here and tortured, dismembered then buried, in a very systematic way.
More than 8000 corpses were dug out and a memorial pagoda has now been built. The contrast with the charming rural nature that has taken over is stunning, but there isn't a lot to see actually, it's more of a way to grasp the paradoxes of this country.
Southern suburb, some 10 kilometers from the city center. Head along the main road out south, then it is indicated at a fork which you take to the left.