The fortress town of Terezin in the Czech Republic was used by the Nazis as a Jewish ghetto during WWII (they called it Theresienstadt). Of the 150,000 Jews who were held there, about 33,000 died in the ghetto itself and about 88,000 were deported to extermination camps such as Auschwitz-Birkenau. When I visited the temperature was about -12 °C; my breath was freezing on the back of the camera, forming a layer of ice that I had to chip off the LCD screen. I was the only visitor that day, and I can honestly say that it was a terrifying experience. See also the Auschwitz-Birkenau gallery.