The Fortress can be visited
Fortress Germersheim-Arresthaus

The Germersheim-Arresthaus Fortress is part of the former royal Bavarian Fortress of Germersheim, located in Rhineland-Palatinate. This complex was a central component of a fortress system built to protect against anticipated French attacks.
History+
The origins of the fortifications in Germersheim date back to 1792, when the French erected new structures, which Bavaria reinforced from 1814. In 1815, the German Confederation recognized Germersheim's strategic importance as a hub for troop deployment in the event of a French attack. Initial surveys began in 1818, but the decision to build a fortress was not made until 1832. Under the direction of Friedrich von Schmauß, construction began on June 30, 1834, with the excavation of the main moat. The foundation stone was laid on October 18 of the same year.
Source: Wikipedia · Licence: CC BY-SA 4.0
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: 49.2193, 8.3759