Built between 1528 and 1536, The Zwinger originally served as a round fortress bastion for the…read morecity's defenses. The building was converted into a prison in the 18th century. During the National Socialist era, the Gestapo seized the building. They used it as an official detention center, emergency jail, and an execution range. The Gestapo carried out numerous executions here, primarily targeting Soviet prisoners of war and foreign forced laborers. Allied bombs severely damaged the site in 1944 and 1945, yet the Gestapo continued using the ruined structure for executions until the very end of the war. Today, the Zwinger is preserved as a memorial for the victims of National Socialism. Rather than being rebuilt, the ruins are left intact to encourage historical reflection. (Google) This is located along the Promenade on which bicyclists traverse. You can't miss it. https://www.tracesofwar.com/sights/15851/Zwinger-Prison-Münster.htm