If you walk the streets of Berlin, you will come across the famous "stumbling stones", or Stolpersteine. They will not literally make you stumble - but they are meant to make your mind stumble.
Just under 10 sq cm, easy to miss, they are small brass stones, embedded underfoot in the cobblestones of the street. Each commemorates a Holocaust victim in front of their last-known freely chosen place of residence. Stolpersteine are meant to commemorate all victims of Nazi Germany. The stones honour Jews, Sinti and Roma, and other people who the Nazis labelled "asocial".