The recent history of Cambodia is pretty torrid. King Sihanouk was deposed in 1970, while on a trip to Paris, his cousin Sisowath and army general Lon Nol took over with US approval, beacuse of their perceived strong stance against Vietnamese communist insurgents. As a result, the Vietnamese troops allied with the communist factions in the countryside. King Sihanouk was in exile in Beijing, having been tried and senenced to death in absentia, and formed an alliance of convenience with the rural resistance factions, who he nicknamed the Khmer Rouge. This group, led by Pol Pot, used the ties to the royal family to grow from a small Marxist faction into a heavily supported armed resistance movement. Lon Nol's regime was apparently pretty corrupt and ineffective, and the Khmer Rouge, hardened by years of US carpet-bombing in eastern Cambodia, captured large parts of the country in a brutal insurgency. In 1975, after years of fighting, Phnom Penh finally fell, and there was initially celebrating in the streets - the Lon Nol government was widely disliked. However, within a few weeks, the Khmer Rouge had shown it's true colors - purging it's ranks of royalists and reverting to fundamentalist Maoism. Phnom Penh was depopulated, and all its inhabitants separated, and forced to walk into the countryside - sometimes hundreds of kilometres - to work on small subsitence farms. Dissent, weakness, sickness or failure to work productively were treated as 'economic sabotage' and were punished with death, as was any hint of resistance to the ruling government. Money was done away with, and the calendar reset to zero - banks were blown up with explosives, but most of Phnom Penh remained as a ghost town. It's hard to believe that all of this was happening while we were growing up in the 1970s.

The KR were unbeliveably brutal. The whole system ran on institutional violence, and it seems like it was only a matter of time before any one individual would break the rules, or be named in a friend's 'confession' and be sent off for 'questioning' and 'relocation'. Estimates of the number of people killed by the regime vary, but the UN consensus hovers around 2 million (and this was out of a total population of only 6 million at the time!), over just three years. This mass extermination required some serious infrastructure; Choung Ek and Tuol Sleng are the capital's two most famous monuments to the sick and psychopathic organisation that was the Khmer Rouge, and their brutal machinery of death.

Choung Ek is one (and only one!) of Cambodia's Killing fields - there are some 340 dotted around the country. You drive down a dirt road to see a large white stupa (memorial tower) rising out of the grounds, with a bright yellow roof. We paid the entrance fee and met a local guide, Suong, and then walked through the entranceway. The gardens are lawned and manicured. Birds and cicadas fill the air with the sounds of the countryside. In an adjoining property, a bunch of schoolchildren were playing a rowdy game of football. It seems such a peaceful place, and as you walk up to the memorial, a lady dressed in white hands you some incense to light. You look up at the stupa - which is about 20m high, and you're suddenly chilled by the fact that hundreds, maybe thousands of human skulls are looking down at you.

It's quite a shock. There some kind of visceral reaction to it that's difficult to describe. I listened in a bit of a daze as our guide described the construction of the memorial. In 1980, the killing fields were discovered. The chemicals poured into the mass graves had lost their effectiveness, and the smell of thousands of decomposing bodies drew people to the site to investigate. They've uncovered about two-thirds of the graves for the memorial - judt under fifty lie untouched. The remains of the exhumed bodies have been carefully stacked into this tower, which is five metres square at the base, and rises up in 17 levels. The number seventeen was picked for two reasons; to commemorate the 17,000 people killed here, and also to remember April 17th, 1975 - the day that Pol Pot took power and began his dehumanisation of Cambodia's society. The clothes of the victims have been disinfected, and placed in the bottom level - children's shoes jumbled together with the garments of whole generations, as youth or old age gave no protection for individuals whose families had fallen foul of the regime. Next come the skulls, demographically sorted, with perspex placards listing descriptions for various groupings such as; "Cambodian, female, juvenile 10-20yrs". It's really hard to see. Our guide pointed out the different wounds on a set of skulls in front of us. "See," he said, "this one was killed by a spade. This one by breaking the skull. And this one - see the bullet hole? That's unusual, they didn't normally want to waste bullets, but at least it was quick."

I really didn't want to take any photos, but Suong encouraged me to do so. "It's important that people see and understand," he said. "Because othewise this could happen anywhere." He then told us that his uncle's family were in there somewhere. "My parents were lucky," he said. "After we'd been made to walk to the villages, we stayed and worked for a few months. Then the Angkar ['Organisation'] said that any intellectuals should return to Phnom Penh. They were needed, and wouldn't have to work in the fields anymore. But a schoolfriend of my father's had joined Khmer Rouge, and warned him not to go. We didn't have time to warn my uncle, he believed they would have a better life. The Angkar promised them a new house." He paused, looking across at the stupa. "This was his house in the end. Him and many, many others."

We walked around the back, feeling quite shaken, to the site of the mass graves. They look like huge craters carved out of the ground, although they're now covered with grass - some of them are four or five metres across. As we got closer, we saw that the entire site was covered with butterflies of every color - pink, white, orange and black. I looked across at Suong but didn't have to ask the question. "Everyone asks," he said. "But the buddhists believe that these are returned souls; of the people who lost their lives here." I looked down at the ground, and realised that the bits of glinting white on the ground were not rocks, but actually fragments of bone, polished smooth by the footsteps of thousands of visitors. A strange shiver passed all the way up my spine to the top of my head - it was an eiree feeling that's hard to put into words; but something profound happened, and is still happening, here.

Suong walked us around the field to the front - pointing out some of the sites of particular tragedy:

"Here's the lake. There are thousands of people left under there, but we leave them to rest."

"Here is the tree where they would kill the infants by bashing their heads in. Or sometimes they would throw them in the air and catch them on a bayonet. They didn't want to leave any survivors from the family, you see, in case of revenge."

"Some of the bodies had no heads. They would normally be Khmer Rouge officers, and they didn't want the people digging the graves to see."

We finished the circuit at a pavillion which was built on the site of the old Choung Ek office. It was here that prisoners would be forced to sign their own death warrants. In Soung's words; "They had to agree to be killed, you see. But many of them had been in detention and torture for months, and so they were quite relieved to see it end." The pavillion has a plaque with a bitter summary of the brutalities of Pol Pot, and an exhortation not to forget them. The English translation is bad, but somehow makes it all the more poignant. Two lines sum it up for me:

"The method of massacre which the clique of Pol Pot criminals was carried upon the innocent people of Kampuchea cannot be described fully in words because the invention of this killing method was strangely cruel so it is difficult to determine who they are for. They have the human form, but their hearts are demon's hearts."

It's hard to understand how this could have lasted for so long, and in a country with (as far as we can see) such open and friendly inhabitants. All these people murdered, and killed by young countrymen or women who'd been sucked into the system, often to become victims themselves as the result of some midemeanour in carrying out their day to day duties. But despite the terrible events that happened here, there is something cleansed and strangely beautiful about the shrine at Choung Ek, and we left feeling slightly changed, as though we'd touched on the best and worst mysteries of human nature in that place.

Our driver took us back into Phnom Penh proper, and we travelled most of the 15km in silence. We then stopped outside Tuol Sleng museum, which was the site of Pol Pot's S-21 security prison, the main torture & detention centre. The site used to be a school until its appropriation by the Angkar, and if you blur your eyes against the barbed wire it still looks like one - with trees, lawns and neatly laid out buildings.

About 17,000 people passed through this prison, without a single escapee. Almost all the occupants ended up under the ground at Choung Ek, and there were only seven survivors when the Vietnamese liberated the prison in 1979. Again, we went around with a local guide, Tivi, and she recounted her own memories of the war years for us - she remembers being rousted out of the house with her family, and made to walk to a village in the south-east, a journey of some 70-80km, which she traced out for us on a map. "One day they killed my father for causing trouble," she said, "and my brother and sister for trying to help him." She and her mother had then fled on foot to the Vietnamese border, a further 30-40km, where they lived in a refugee camp for four years. "I've worked here ten years," she said. "But my mother has never been to visit me. I don't blame her - it's hard to remember what happened every day, but I don't want to forget." She then showed us around the prison itself, and I don't think I'll ever forget that place, as long as I live.

We started off in Block A, which housed the 'VIP' prisoners - normally Khmer officers who'd commited an infraction or come up in the confession of a friend or acquaintance. As VIP's they had their own room, with a single bed. The bed was rusty metal, though, and the prisoners were permanently shackled to it. They were also given a small metal bucket as a toilet, instead of having to use the floor like the common prisoners. "They would even given them a blanket, and a mosquito net," Tivi told us. "But they would still be tortured every day." It was shocking to see the rooms, which had been left in their original state, and had large photgraphs in each cell showing the last inhabitants of the rooms as they were found after the liberation of Phnom Penh - still shackled to the beds, throats slashed or heads smashed in. In fact, the second room still contained the shovel used to kill its last occupant - casually discarded in the corner, and clearly the same utensil depicted in the 1979 photograph on the wall.

From here, we walked though into the common cells. 8-10 prisoners would be crammed into a filthy space the size of a large toilet cubicle. There were no doors, as the prisoners were permanently chained, and killed if they talked to each other. It must have been terrible for those people - crammed into alcoves in shackles, unable to talk or move very far, with an open door and sunlight just a few metres away. There was barbed wire blocking off the balconies, but as Tivi said, " Not to stop escape - no-one ever escaped. This was to stop them comitting suicide."

We then went through into the galleries. The prison adminstrators were meticulous about record-keeping, and there are 4-5000 pictures of the camp's victims pasted to freestanding boards. There's no discrimination - men, women and children are all included, with precise front facing and profile shots; there was a special chair to hold the subject's head in precisely the right position. Some of the babies in the photographs were too small to sit up and had to be held by their mothers, but still needed their own photos. There's one really poignant picture of a mother holding her baby with a single tear running down her face. "She was the wife of a Khmer government minister," Tivi said. "He was taken in for questioning as a traitor, and so was she. She's crying because she already knew about what happened at this place, and that she would not come out alive, or her little son."

In the next gallery was a board of young, smiling Cambodian teenagers. I was puzzled that they all had the same haircut. "They are the interrogators," Tivi explained. I was actually stunned by this - I suppose I'd known that they must have been young, but I was amazed that they looked so innocent, and that there were so many of them. "They needed many," she said. "They'd get them from the village as children and train them. But if they broke a rule, or broke a piece of equipment, or didn't want to torture a friend, then they would stay here, but on the other side of the door - with no clothes and wearing a shackle instead, and the Angkar would need a replacement. But some of them survive, and they are living back in the villages today."

The thing that keeps coming back to haunt me about Pol Pot's regime is it's cannibalistic nature. It seemed to feed on fear, violence and suspicion, and it was so embedded in the system that no single individual could avoid it, or actively change their role with it. They were either a perpatrator or a victim, and often both, in this sick society that subverted the humanity of entire generations.

There hasn't really been any closure for Cambodians on the events of the Khmer Rouge rule. A couple of trials have taken place recently, but Pol Pot was alive and well until 1997 - leading the Khmer Rouge and destabilising the whole country from his base in Thailand. Eventually his paranoia got the better of him, and the brutal execution of Son Sen (KR defence minister) led to his overthow by Ta Mok, the KR general who led most of the rural pacification exercises (read genocide). Ta Mok sentenced Pol Pot to lifelong house arrest, but he died in the NorthWest in 1998 in slightly suspicous, although apparently natural, circumstances. Ta Mok himself was later arrested, but never completed a trial - dying in 2006. I don't know enough about the situation to really understand it, but there seems to be lot of anger at this unresolved situation bubbling away under the surface, and there's limited time to sort it out before all the participants disappear from old age. Hopefully, however, it's a chapter of the country's history that's closed forever.

We finished off at Tuol Sleng walking through some of the later galleries. Two of the seven survivors were painters, kept alive to churn out complimentary portraits of Brother No. 1, Pol Pot. They've turned their talents to reproducing some of their memories of S-21, a harrowing and graphic display of torture, rapes and murders - the daily grind at this former place of learning. There were also some 'then and now' pictures of the camps staff - cooks, mechanics and even interrogators. It brings home the awful nature of this system to see the interrogators' mugshots next to photos of them playing with their children, and to see a short recounting of their time here, where they all said the same thing; "I didn't want to do it, but what choice did I have?". Most of them seem to want a trial or truth commission to explain their actions and, like the rest of Cambodia, get to grips with what happened here. There's nothing of the slightly sacred feeling at Choung Ek - the pain and terror are still in the air at Tuol Seng - it's a reminder of the worst things humans can do to each other, and to themselves.

Feeling very overwhelmed, we went back to our hotel, and cleaned up. We'd made plans to meet Jet & Sauli at a restaurant in town, and looked around us with a different eyes at the city that had been emptied in a matter of days just over thiry years earlier. Cambodians seem to have shaken it off and moved forward, though - they are a really warm people; always interesting and great to talk to. We had a great dinner & conversation, and then a couple of drinks at the FCC rooftop bar before heading home ... looking out over a city and a country that seems to have pulled off an amazing recovery.