The remains of the fortress can be visited
Fortress Koblenz-Arzheimer Schanze

In today's Koblenz district of Arzheim are the few remaining remnants of the Fortress Koblenz-Arzheimer Schanze, once a component of the Prussian fortifications.
History+
The Arzheimer Schanze was provisionally constructed in 1866 before being permanently expanded into a lunette between 1868 and 1873. It was an integral part of the Niederehrenbreitstein system within the Fortress Koblenz. After World War I, the Treaty of Versailles led to the de-fortification of military installations. The demolition of the complex began in March 1927 and was completed by August of the same year.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://de.wikipedia.org/wiki/Datei:Arzheimer_Schanze_01_Koblenz_2014.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: 50.3591, 7.6218