The remains of the fortress can be visited
Fortress Koblenz-Werk Pleitenberg

The Pleitenberg Work, a defensible powder magazine, was part of the Prussian Fortress of Koblenz. It secured the plateau north of Ehrenbreitstein Fortress.
History+
The construction of the Pleitenberg Work took place between 1827 and 1830. It was conceived in the 1820s as part of the Fortress of Koblenz and was last modified in 1891. Together with Fort Rheineck, it formed a defensive line, reinforced by earthworks and later added concrete fortifications. After World War I, in accordance with the Treaty of Versailles, the facility had to be de-fortified and largely demolished in 1927. Although many parts were removed, the hangar remained and was later used as living space.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://de.wikipedia.org/wiki/Datei:Koblenz_im_Buga-Jahr_2011_-_Festung_Ehrenbreitstein_15.jpg
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: 50.3711, 7.6218