To be privately owned
Fortress Koblenz-Fort Rheinhell

Fort Rheinhell, a part of the Prussian Fortress of Koblenz, was a military structure on the Pfaffendorfer Höhe. Although built in the 1860s and largely dismantled in the 1920s, sparse remains still show its presence in the Koblenz district of Asterstein.
History+
The origins of Fort Rheinhell date back to after 1859, when it was initially established as a provisional earthwork south of Fort Asterstein. Between 1864 and 1868, it was permanently expanded into a lunette. A connection to Werk Glockenberg was established in 1864. After World War I, Fort Rheinhell, like many other Koblenz fortifications, had to be disarmed in accordance with Article 180 of the Treaty of Versailles. Destruction affected ditch walls, caponiers, powder magazines, and hollow traverses. Despite the planned breaches in the connection to Werk Glockenberg, a request was made to preserve the casemate in the rampart, as it was to be used by a dairy cooperative.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://de.wikipedia.org/wiki/Datei:Rheinhell.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: 50.3494, 7.6144