"...It must be an amazingly awful place to visit..."
In one sense it wasn't. I walked there on a bright summer morning, arriving at the gates of Birkenau first, it was sunny, the grass was long, birds sang and there were thousands of butterflies and other insects fluttering around. The scale of the place is hard to imagine without actually being there, you can enter the gatehouse building and look around, I was struck by how normal the building looked, there were mains points, light switches, the walls were painted in some depressing office color just like any old military building or barrack in the UK. The surviving sheds in the Birkenau camp would also be familiar to anyone who spent time in old army buildings, many still had the plumbing fixtures in place. A lot of logistics I thought at the time, to get all that stuff there and built, that took some planning, not planning by monsters or aliens, but by bureaucrats and civil servants.
The Auschwitz main camp already existed prior to the war, these are brick buildings and host the 'museum' proper. Different countries have a holocaust related exhibit in some of the buildings. In one room there was a chamber filled with human hair, that did it for me I think.