The City Wall can be visited
City Wall Düren

The district town of Düren in North Rhine-Westphalia was once protected by city fortifications, which are only partially preserved.
History+
Düren, first mentioned in Frankish imperial annals in 747, developed into a fortified place. As early as 1226, it was referred to as “oppidum nostrum Duren”. According to tradition, the construction of the city wall began in 1224. The first city gate, the Holztor, was mentioned in 1261, indicating an already existing fortification. The medieval wall was built from variegated sandstone blocks and reinforced in the 14th century with flying buttresses to increase its stability during bombardment. From 1493, round bastion towers made of brick supplemented the defensive structures. A drawing by Wenzel Hollar from 1634 provides information about the course of the wall and the locations of the gates at that time. Many towers, such as the Schellengassenturm, Münchenturm, and Pulverturm, have disappeared today. Others, like the Dicke Turm and the Grönjansturm, are still preserved, as is the Spießenturm, which was recently renovated. A double ditch system and a rampart also belonged to the fortifications. Remains of the five-meter-deep city moat were uncovered in 2011.
Image: http://www.wehrbauten.de/thread.php?threadid=570
Location: 50.7991, 6.4820