I went to see Auschwitz-Birkenau a few years ago. Of all places in the world that I have been, this would have the most vivid memories. There were many sights there that day that would take the immediate eye, but if you looked hard, you could see other things. One such thing I remember was walking into a Birkenau hut. The huts had a row of glass windows like skylights that ran the length of the buildings. Just above the doorway was a 9mm bullet hole. I pictured it as it had happened. A guard had thrown open the doors and shouted for the prisoners to hurry, then drew his pistol and fired it at the ceiling to make his point. The hole remains forever as a testament. Another was a rifle rack in Hut 12 at Auschwitz. There are others. Go there and see what you can see. Everyone should go.