I spent a day going to S-21, the high school-turned-prison/torture chambers during the Khmer Rouge, and the Killing Fields. I felt sick to my stomach all day and became teary-eyed more than a few times. Over 2 million people were killed during this regime from 1975-1979. The atrocities that some humans are willing and able to commit are incomprehensible. And it still exists today (most notably in Sudan - if you want to get involved with a reputable group that is working there savedarfur.org is a good one). I just don't understand how the world community continues to let genocide occur again and again... I'll get off my soap box before I really get on it, but see below.
some photos of the victims held at S-21 before they were executed
barbed wire covering the outdoor hallways at S-21
one of the small holding cells
skulls found in the Killing Fields (i spared you the close up shot I took where you can see the bullet holes and marks from the bludgeons; many people didn't get the mercy of a precious bullet -too expensive)
a mass grave
all these depressions are mass graves