ON Monday this week, I spent the day at the world’s largest cemetery and mass grave – Auschwitz-Birkenau in Poland. There can be no greater monument to man’s inhumanity to man than this Unesco World Heritage site, rightly preserved and maintained for future generations.

Walking between the blocks, seeing the piles of shoes and suitcases, shaving brushes, children’s hair tresses and a tangled tower of spectacles; then pausing at the main square with its gallows where prisoners were arbitrarily put to death in front of fellow inmates lined up for roll calls which lasted sometimes a full day, it is of course impossible not to wonder at mankind’s apparently endless capacity to kill and destroy.

The most commonly asked question by the hundreds of thousands of people who visit the sites (Auschwitz work camp and the Birkenau extermination camp are separated by some kilometres) is, understandably, how did the Nazis get away with it – how did no-one know what was going on? Of course, in the days before rolling news and the internet, it was so much harder to disseminate information – that is one reason. But the other is that the scale of the atrocity (1.2 million died in Birkenau) was simply too immense for people to compute. As the news leaked out during the war, those telling of the horrors were simply not believed. One Polish resistance fighter took the staggeringly heroic decision to get himself arrested in order to be sent to Auschwitz, where he spent the next two years gathering evidence of the atrocities being carried out. When he escaped and told his tale, he could get no-one to believe him - and after the war he was executed as an enemy of the state by Stalin.

It is a testament to the fortitude of the Polish people that places such as Auschwitz remain today, in order to educate the generations that came behind about the evil man is capable of. How much easier it would have been to raze Auschwitz and Birkenau and, in modern parlance, “move on”.

Sadly, of course, no amount of moving on can prevent acts of atrocity and terrorism. “Never again” is an easy platitude; but while it is safe to say no genocide will ever again be perpetrated on the scale of the Holocaust, the victims of the Kosovan war and, today, Syria, know only too well that man’s hatred of “the other” continues to plumb untold depths.

It seems odd to describe Auschwitz-Birkenau as a visitor attraction but, by dint of the sheer scale of visitors who make the pilgrimage to it each year, that is what it is. Before entering the camp and walking under the infamous “arbeit macht frei” sign, it is possible to buy Auschwitz memorabilia – including fridge magnets and miniature replica “death gates” – which I found both bizarre and utterly tasteless – but such is the modern need to be able to say “I was there”.

It does of course go without saying that while the vast majority of visitors took in the tour in near silence, with some in tears, for others it was an opportunity to get the selfie sticks out and grin bovinely, as I saw one visitor do, in front of a cattle truck on the Birkenau rail track. Hard to imagine what the Jews who were herded to their deaths there would have made of such stupendously crass behaviour.

As harrowing places to visit go, this is as bad as it gets. At the height of the Holocaust, 25,000 people each day were being brought in to Birkenau and killed. That this happened in such recent times – millions of people alive today were alive during this hellish period – is perhaps one of the most sobering aspects of a visit to Auschwitz.

It is important to honour and pay homage to the great and noble things of which man is capable – the world is full of man-made wonders and truly life-enhancing inventions – but it is equally important to acknowledge the depths of depravity to which man is also capable of sinking.