Recently I read Viktor Frankl's "Man's Search for Meaning", and it got me thinking. It's hard for me to imagine that so many horrible things could a) happen at all; b) that humans could be capable of such industrialised sadism and murder; and c) that the place where all of this happened still exists in some form, somewhere in the world. I see the numbers (1.3 million in Auschwitz; 150,000 in Chelmno; 200,000 in Dachau) but the real-world logistics of it all goes beyond what my sheltered little middle-class mind can process. For instance: in 1944, somebody had the job of driving the gas van at Chelmno, hour after hour, day after day, presumably taking coffee breaks, making inane conversation with workmates, and thinking about what he was going to do when he got home. He got up every day, got dressed and had breakfast, then went to work and gassed vanloads of prisoners - men, women and children - to a slow and painful death. This guy existed. He wasn't some maniacal, wild-eyed psychopath who bathed in virgin's blood; in all likelihood, he was a normal-looking everyman who presumably laughed at jokes, had a favourite movie, and worried about his expanding waistline or emerging pattern baldness. It's this part of genocide that I least understand. In my mind's eye, the sky during the Holocaust was always grey and gloomy, there were no plants, and this was playing at all times.

Which might be why encountering the real remnants of genocide is so striking. I haven't been to Auschwitz, but a few years ago I paid a visit to another little slice of pure evil - Cambodia's Tuol Sleng Prison, the Khmer Rouge's torture and extermination site for some 17,000 political prisoners in the 1970s.

Tuol Sleng sits in the middle of an unremarkable section of Phnom Penh, down a two-lane sidestreet and surrounded by other similar industrial buildings. In its previous life, Tuol Sleng was a high school; indeed, it continued to be run by a schoolteacher during its "management" by the Khmer Rouge (want to see the face of sadistic cruelty? That guy). Three main blocks surround what used to be the sports field; administration buildings sit near the entrance.

40-odd years later, from the outside it still felt like a high school. Unfortunately, it's probably the only high school in the world with classrooms still bloodied from their use as torture chambers.

If the raw reality of the torture chambers proved too much, you could always go outside for a breath of fresh air next to the gallows where countless prisoners were hanged. No? How about next to the pots where they used to drown them?

The main block of classrooms has been converted into the genocide museum proper, and the walls are lined with the intake photos of those unlucky enough to have visited at the wrong time in history. Thousands of expressions of fear and dread. The yearbook from hell.

For a vast majority of prisoners, weeks or months of extreme daily torture came to an end with a short ride to Cheoung Ek, "The Killing Fields." Or in other words, a paddock of a few acres surrounded by trees, next to a rural primary school. I could have been standing in a park in Geraldine, except for the tomb of 5,000 skulls, the dozens of burial pits, and the small pieces of human bone (read: teeth, fingers, toes) strewn across the tracks.

A bunch of schoolkids were hanging out by the fence that casually bordered their sports field and the mass grave of several thousand people. An old German tourist (Germans, seriously, what is wrong with you) was doing his best to cajole them into singing a song so he could take a video. For some reason this is my most vivid memory of the killing fields; here was the closest thing to evil in tangible form, the setting for mindbending cruelty, yet nobody seemed to be grasping the significance of it. Myself included: it was all much too everyday and bland and normal-looking. But then what was I expecting to see? Black clouds and smoke rising from the ground? It's a hard conflict to shake. And it highlighted to me that even coming face-to-face with the evidence of genocide brings you no closer to understanding how any of it could really happen.