It was a devil to find. And that is what its creators had intended. Treblinka II, the Nazi extermination camp north-east of Warsaw, was the ultimate expression of the Final Solution. It is estimated that in the space of 13 months (July 1942-August 1943), at least 780,000 people were gassed or shot there. More people died at Auschwitz-Birkenau but over a longer period. This was the SS killing machine at its most efficient.

The enormity of the Nazi project - to rid Europe of Jews - was wreathed in subterfuge. Those at the apex of the Third Reich ensured that their signatures were not on the relevant documents. The sites chosen for extermination were remote and heavily camouflaged. In 1943, as the Soviet armies approached, Treblinka II was dismantled, the ground was ploughed over and a Ukrainian guard was settled there as the resident "farmer". After he had left, local people unearthed parts of decomposed bodies. But it required the witness of survivors, some of whom had escaped during a brief uprising in August 1943, to reveal the full extent of the horror.

Our approach to the camp was complicated because the road from Malkinia Gorna, which takes you southwards over the railway line and the River Bug to the village of Treblinka, was closed for repairs. After trying to find the way, we were directed back downstream to Brok, where we crossed the river. Reaching the village from the west, we found no signpost to the former camp, so headed south. After a mile or so, we realised we had overshot. We came back and this time noticed a little black sign pointing to the left. We had at last found what we were after. Unlike Auschwitz-Birkenau or Majdanek, an extermination camp on the outskirts of Lublin, Treblinka II has none of its original buildings. Today, what was there is symbolised by stones. Before you reach the "entrance", tablets in English, French, German, Polish, Russian and Yiddish remind you of what happened - the liquidation of around 800,000 Jews, first from the Warsaw Ghetto, subsequently from other parts of Poland, then from Austria, Belgium, Bulgaria, Czechoslovakia, France, Germany, Greece and the Soviet Union.