Auschwitz exerts a gravity of its own. You can travel to Kraków without visiting it, but you’ll remain aware of it, the many signs advertising tours tugging at you, reminding you of the black hole of history, lurking just beyond the horizon.

A friend of mine told me, when I mentioned that I intended to visit the concentration camp, that they couldn’t bear to do so. I can understand that. I’m not the most sensitive person, but even I can’t help but feel unease at the incomprehensible nature of what happened there. Still, I wanted to go, to be part of the effort to remember and not forget, and so I did.

(Apologies is some of the below is upsetting.)

That the visit was on the warmest, sunniest day I’d experienced in years was somewhat incongruous. In fact, the whole start of the tour, around the original Auschwitz I camp, felt a little off at first. To sanitised, too carefully restored and preserved, too occupied by tour groups. I was beginning to wonder if I was missing something. Then we reached the room full of human hair.

In one of the restored barracks buildings, fully half of a long room was taken up by a mass of human hair, taken from the scalps of the dead, with traces of Zyklon B still detectable when the Soviets liberated the camp. In further rooms were the dead’s belongings: eyeglasses, coats, suitcases with names written on them, shoes, children’s shoes. As much as anything else, the weight of these objects lay in the fact that they were the only remaining scraps of evidence that the Nazis hadn’t gotten around to destroying or using

We had been meant to see these first – a long queue meant that our guide took us around those more sanitised buildings first. Like some of the concentration camp victims, I was lulled into a false sense of security, feeling that seventy years since the camp was liberated had deprived it of its power to shock. Preserved behind glass though it may be, it still reaches out.

A mile or two down the road from Auschwitz I is Auchwitz-Birkenau. Dreadful as it was, Auschwitz I was in effect a trial run – Auschwitz-Birkenau is an order of magnitude larger and was the place that the Nazis applied industrialised methods and an inhuman level of detachment to their “final solution.” Here, though they tried to burn and demolish the traces of what they’d done, can still be seen the ruins of the crematoria and the shells of the barracks that housed the dying and the doomed.

Auschwitz I retains the indelible image of all that the Nazis took from their victims. Auschwitz-Birkenau demonstrates the scale to which they brought that collective sin. Moreover, it’s the decaying nature of Auschwitz-Birkenau that lends a final reminder of reality: this is not a preserved exhibit in a museum. This is a place where more than a million people were murdered. It needs to be remembered and I’m glad I visited, though that visit will stay with me.

If there was one thing that I missed, it was some sense of why this happened. Auschwitz preserved the “how,” but it makes less effort at showing how a nation can slide so irrevocably into horror. How centuries of looking down on Jews and other “others” curdled into contempt and hatred. How political leaders could take that hatred and bind it to a “solution” that led step by step to Auschwitz-Birkenau.

At a time when Europe and the U.S. are convulsed with fear of immigrants, and when our politicians are advocating ever more draconian measures to deal with this problem, we need to remember where that path leads. We already have them in camps, after all. We are hearing calls for them to work for their keep, to earn the right to live among their betters. It’s a reasonable proposal, isn’t it? It always is, at the start.