Zwinger, Defensive tower in Münster, Germany

The Zwinger is a round bastion of the early modern Münster city fortifications, 24.3 m in diameter with an outer wall about 1.95 m thick. Inside, two upper floors, a cellar and a separate attic once surrounded a central courtyard, with six cells per floor after the 1730s conversion into a prison. Allied air raids in World War II left only parts of the original structure.

The Zwinger is a roundel of the early modern city fortification, built in the 1530s. Prince-Bishop Franz von Waldeck had it made 'mightier' between July 1535 and March 1536 by adding a second wall about 2.2 m in front, creating the ring passage. In the 1730s it was converted into a prison with six cells per floor around a courtyard; in 1919 it was rented as a dwelling and studio for painters. Under the Nazis it served as a Gestapo prison and execution site, and Allied air raids heavily damaged it.

The Zwinger holds Rebecca Horn's sculpture Das gegenläufige Konzert, added when the building became a memorial. Two mechanical hammers strike the walls in opposing rhythms, so the piece plays the former Gestapo prison itself as an instrument. The memorial belongs to the Stadtmuseum Münster, and the sculpture's title refers to music set against violence and tyranny.

The Zwinger stands on the promenade ring that replaced Münster's fortifications in 1772; the ground around it was lowered then, so the former entrance now sits well above street level. The round walkway between the outer wall and the inner ring of cells is the part to look for. The building belongs to the Stadtmuseum Münster, which holds the key to opening times and guided visits.

The Zwinger is a roundel 24.3 m across, wider than the better-known Zwinger in Goslar, with outer walls about 1.95 m thick. Max Geisberg argued in 1932 that the wall was originally up to 4.64 m thick and was partly removed in 1732. The nickname 'Dat grote Bollwerk' refers to this mass.