Phnom Penh, Cambodia: Pol Pot's brutal regime.

From the beauty of Angkor we headed south by bus to the capital Phnom Penh. Without question the most noteworthy story to tell was the day we visited the Killing Fields and the old Tuol Sleng prison. I'd read a little about the astonishing brutality and mindless genocide of the communist Khmer Rouge's ill-fated years of power in the late 1970s but visiting such key sites made everything immediately more real.

The Khmer Rouge regime killed more than one and a half million of their own people - about a fifth of the population - as it sought to turn Cambodia into a mass agricultural commune where everybody pulled together on farms and forced labour projects. Those seen as intellectual, mildly clever and even wearers of spectacles were viewed as highly undesirable and were by and large executed en masse. City dwellers, professional people, anyone with an education - if you had more than a few brain cells to rub together then the Khmer Rouge, led by Pol Pot, did not want you around. Phnom Penh literally became a ghost town as city folk were driven away. Illiterate rural peasants were seen as the true proletariat and most others were wiped out.

The Killing Fields is a site outside Phnom Penh where the Khmer Rouge executed an estimated 200,000 people in multiple mass graves. Today you can still see fragments of clothing, even human bone, poking out from the soil. Most harrowing of all, a commemorative stupa now stands as a memorial to those who lost their lives. Unlike most memorials, its graphic and real, containing numerous glass shelves each housing the skulls of scores of murdered Cambodians. This contrasted with the noise of children playing in a nearby school serves only to emphasise the horrors of the past and makes you wonder how on earth this could happen in a country filled with such happy people. It sounds so barbaric, yet this was well after Hitler and the Holocaust, happening just a few years before I was born. A visit to the Killing Fields manages to be both deeply chilling and yet oddly serene in its now peaceful, leafy location.

Precious little serenity to be found at Tuol Sleng though. Tucked away down Phnom Penh side streets, this former school was turned into Security Prison 21 (S21) by the Khmer Rouge. As many as 20,000 prisoners were thought to have been held here - many of whom were tortured and forced to confess whatever made-up charges were put in front of them, or name friends and family who would then be brought in too. One wing features black and white photos of decomposing corpses laid out on metal beds - pictured as they were found when Vietnamese forces discovered Tuol Sleng as they overthrew the Khmer Rouge in 1979. When you look down and see the same checkerboard pattern floor as shown in the photo on the wall it drives home that you are standing in a room where senseless murder was committed. The other wing houses large galleries of mugshots of the dead, with numbers around their necks, part of the Khmer Rouge's strangely diligent system of record keeping. Pol Pot had an eye for thoroughness and detail. He wanted to know what his prisoners looked like, and see proof that they'd been tortured or killed for his own twisted peace of mind.

An enormous monsoon meant we had no choice but to stick around inside Tuol Sleng until it had eased up. The wind howled around the open windows and gave the place an even more eerie quality than it has in the sunshine. Its important that visitors to Cambodia come here and see this. That the country's people can still smile despite the deep scars of a generation ago - wounds that will take many more generations to heal - is really remarkable.

You'd probably hoped I might tell you a bit about what Phnom Penh is like as a city - and it is a charming, hectic place full of lovely people - but its the atrocities of three decades ago that are the real story to tell.