La Risiera di San Sabba, a former factory where rice was peeled and cleaned. This was one of the scariest places in Italy during World War II. The building was used as a concentration camp for non-jewish enemies of the Nazis, and as an intermediate station for Jews, before they were sent on to the Death Camps in the east.
The Italian state has struggled with how to deal with the facility. There were plans to completely raze it, but finally a part of it was turned into a museum.
This is not the original entrance. Neither was the whole facility a concentartion camp. The approach of the architect who built the museum was, to use blank concrete walls for fencing off the prison part. The result looks very different from what it must have looked at the time, but it does a hell of a job expressing the feeling of being locked in.