The City Wall can be visited
Town Fortification Münster-Zwinger

The Zwinger in Münster, a part of the former city fortifications from the early modern period, is located in the city of Münster, North Rhine-Westphalia. It transformed from a bulwark into a memorial.
History+
The origins of the Zwinger date back to around 1528, when it was built as a bulwark in Münster's defense system. During the rule of the Anabaptists in 1534 and 1535, it served them for defense. After the end of this era, Prince-Bishop Franz von Waldeck had the Zwinger converted into a Zwingburg (coercion castle) from 1535 to suppress potential uprisings.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://www.wehrbauten.de/thread.php?threadid=617
This description draws on the facts documented in the linked Wikipedia article; Wikipedia content is licensed under CC BY-SA 4.0. Wording and editing: Mobile History.
Location: 51.9675, 7.6317