Cologne - Stolperstein
Of the four individuals who lived in a house at this location, three successfully escaped to England, and thence to the U.S. The fourth, however, died at Auschwitz.
Wikipedia: "A Stolperstein, literally "stumbling stone", metaphorically a "stumbling block") is a sett-size, 10 by 10 centimetres (3.9 in × 3.9 in) concrete cube bearing a brass plate inscribed with the name and life dates of victims of Nazi extermination or persecution.
The Stolpersteine project, initiated by the German artist Gunter Demnig in 1992, aims to commemorate individuals at exactly the last place of residency—or, sometimes, work—which was freely chosen by the person before he or she fell victim to Nazi terror, euthanasia, eugenics, was deported to a concentration or extermination camp, or escaped persecution by emigration or suicide. As of 23 October 2018, 70,000 Stolpersteine have been laid making the Stolpersteine project the world's largest decentralized memorial."