Cambodia is a beautiful country, with some of the most welcoming people with the widest smiles of any place I have visited before or since.
But it is a country with a past so horrific, so recent, and so terrible that you wonder how people can ever move on.
From 1975 to 1979 Cambodia was ruled by the Khmer Rouge, a party, lead by Pol Pot, based on communist ideals that ultimately resulted in the mass genocide of its own people.
In just four years over 2 million people are estimated to have died in waves of murder, torture, and starvation, aimed particularly at the educated and intellectual elite.
Our first stop was at the Tuol Sleng Genocide Museum, a former high school that was turned into the Khmer Rouge's most infamous political prison.
Here prisoners were detained, tortured until they confessed to their "crimes" before being sent on their final journey to the Killing Field.
Classrooms became cells, crammed full of people, tiny rooms, with metal beds and shackles were still in place, left as they were found. An estimated 17,000 people were imprisoned at Tuol Sleng. Only seven are documented to have survived.
Most victims were from the previous regime and included soldiers, government officials, as well as academics, doctors, teachers, students, factory workers, monks, engineers, etc.
Later, the party leadership's paranoia turned on its own ranks and purges throughout the country saw thousands of party activists and their families brought to Tuol Sleng and murdered.
Upon arrival at the prison, prisoners were photographed and required to give detailed autobiographies, beginning with their childhood and ending with their arrest.
The images that will stay in my mind forever were the final rooms in the museum, empty but for row upon row upon row of black and white photographs of the prisoners. From tiny children to frail elderly people, they stare into the camera lens as if it is the barrel of a gun.
One photograph shows a young woman, a single tear falling down her cheek. Her tiny baby is in her arms.
You know that not one of these people survived. Whether from torture, starvation or being taken to the killing fields, they all came to Tuol Sleng to die.
And you can see in their eyes that they know it too.
Choeung Ek
This is the best known of the sites that became known as killing fields.
The sunlight shone over a field of green grass and butterflied flickered up and down, children played and laughed and it was only slowly that you started to see the mounds, and the bundles of rags under trees.
When I asked the guide what they were he told me they were the remains of the clothing of the people they had bludgeoned to death and pushed into mass graves. If you look at the paths you are walking on, he said, you can still see teeth and pieces of bone.
In the middle of the field stands a Stupa full of skulls. There are over 5,000 human skulls. Many have been shattered or smashed.
I debated long and hard about whether to take a photograph of this. I heard many people say they would not, it seemed wrong, or distasteful or they did not want a reminder of it.
I decided, on reflection to take a picture. If people are horrified so be it, if they recoil then good. History cannot be swept under the carpet and avoided because it is too terrible. These events happened in our life time. These people deserve to be remembered.
In order to save ammunition, the executions were often carried out using poison, spades or sharpened sticks.
In some cases the children and infants of adult victims were killed by having their heads bashed against the trunks of trees. The rationale was "to stop them growing up and taking revenge for their parents' deaths.
As we left the site our guide Mr Sun, a cheerful, talkative man was silent for a while. He then told us the story of how when he was five, there was a knock at the door in the night and they took his mother away. She was a teacher. They never saw her again.
