The Fortress can be visited
Fortress Germersheim-Seyssel Kaserne

The Germersheim-Seyssel Barracks Fortress is a fortification in Germersheim, Rhineland-Palatinate. As part of the former Royal Bavarian Fortress of Germersheim, it played a role in the German Confederation's defense strategy against attacks from France.
History+
Construction of the Germersheim Fortress, financed by the German Confederation, began in 1834. It served to protect against French invasions and was strategically important, as Germersheim was considered a military hub on the Rhine. The construction work lasted until 1855, with the mining tunnels only completed in 1861.
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: 49.2165, 8.3709