The Fortress can be visited
Fortress Koblenz-Batterie Hübeling

The Fortress Koblenz-Battery Hübeling, a historic intermediate work, is a part of the former Prussian Fortress Koblenz. Originally designed as a defensive powder magazine, it now serves as a memorial site.
History+
Battery Hübeling was constructed between 1828 and 1830 and served as a defensive powder magazine. It was an integral part of the Feste Kaiser Alexander system, protecting its right flank and a blind spot below the main fortress. Additionally, it controlled the Moselle River, the riverside road, and the forefield of the Moselweißer Schanze. The structure was a small, detached work with a casemated blockhouse, consisting of a two-story, brick-built gun tower on a slope. It was armed with eight to ten cannons and mortars, plus an infantry detachment. In 1859, a water pipeline was laid from Feste Kaiser Alexander to the battery. In 1903, the facility was abandoned and leased to the city of Koblenz.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://de.wikipedia.org/wiki/Datei:Batterie_H%C3%BCbeling_Koblenz.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: 50.3513, 7.5724