The Fortress can be visited
Federal Fortress Ulm-Ludwigsvorfeste

The Federal Fortress Ulm-Ludwigsvorfeste is a component of what was once Europe's largest fortress system. Located in Neu-Ulm, Bavaria, this structure once served to defend the German Confederation.
History+
The Federal Fortress Ulm, to which the Ludwigsvorfeste belongs, was one of five federal fortresses built after Napoleon's defeat in 1815. Construction of the entire fortress complex took place from 1842 to 1859. The Ludwigsvorfeste itself was built between 1850 and 1853 under the direction of Bavarian First Lieutenants Ysenburg and Dillmann.
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: 48.3831, 10.0085