Angkor Wat is the most famous and spectacular of the temples that surround Siem Reap in Cambodia. I just spent the weekend there, to see something of these building projects of the ninth to eleventh century Khmer kings. They are extraordinary ??" in terms of scale at least, outdoing even the grandest cathedrals of medieval Europe. However, it was not Angkor Wat but another of the monuments in the area that came to carry a particular poignancy for me.

The particular temple I have in mind is called Banteay Samré, pictured above. It is not as impressive as Angkor Wat or others like the Bayon, famous for the serene representations of the god of compassion that push out from its towers, pictured below. On the other hand, Banteay Samré is a little off the beaten track, and freer of tourists as a result.

The temples were symbolic representations of the cosmos, the central towers representing Mount Meru, the centre of the universe in Hindu mythology. These ornate piles are surrounded by shrines and galleries, and Banteay Samré has two such cloisters, one inside the other.

And yet, this particular example of what a civilisation can achieve at its greatest, was also the site of human action at its most depraved. For in the late 1970s, the Khmer Rouge turned Banteay Samré into a prison. The galleries were divided into airless cells: from the temple, was created a hell hole. People were bricked in and forgotten. The day we visited, it was 40 degrees in the shade. Before the monument could be reopened to the public, mounds of human bones had to be cleared from its enclosures and those cells.

Our guide told us about what had happened at Banteay Samré, and like most Cambodians now approaching middle age, he is living with his own memories of the regime. His parents had been teachers and just before Pol Pot began his experiment in agrarian communism, they were savvy enough to leave the university and school where they had taught and take up life as farmers: when the henchmen came to call, they had calluses on their hands and so could ‘prove’ they were not intellectuals.

He was separated from his parents and moved to a commune of about a thousand children. During the next few years, his four sisters all died, along with many hundreds of others. Famine was the big killer, along with hideous punishments.

One day, driven by hunger, he told us about stealing some potatoes with three other boys. The three were caught, and shot, their bodies tossed into a ditch. He escaped only because, on impulse, he came back by a different route. Another day, one of the men in charge of the children asked the commune commander whether rations might be increased, since so many were dying. The commander decided to make an example of the man. He ordered someone to cut down a dead palm branch, the edges of which are as strong and sharp as a notched sword. As the children watched, the man had his head cut off, by degrees. Every time he passed out, he was revived with water.

Angkor Wat itself carries scars from the time too. For one thing, there are shrapnel marks on the walls. But again, our guide pointed us to a particularly grizzly detail. One of its gallery walls depicts the levels of hell in detailed bas-reliefs. As you descend, the tortures become more brutal. Close to the abyss are images of victims being tied to frames with nails driven into their arms and legs. The Khmer Rouge stole the idea: in real life, there was a nail for every question someone couldn’t or wouldn’t answer.

Cambodia has been open to the outside world for about a decade since those times. Poverty is still omnipresent, though the population is booming, as is tourism in places like Siem Reap. Corruption seems to be the biggest problem people face today, which whilst bad is a step forward compared with killing fields.

Will there be a truth and reconciliation commission, we asked, seeking signs of hope after the evil? Many of those who committed crimes must still live in the country. (Pol Pot himself died in 1998, never having been put on trial; to date, I believe, only a handful of his cadre have been found guilty and jailed.) Our guide smiled. Most people want to put these things to the back of their minds, he explained.

It is a wonder of the human spirit that he could smile at all. And he turned our attention from the horror, back to the beauty of Banteay Samré and the high point of his civilisation.