The Fort can be visited
FortressSande - Mariensiel
Fortress Wilhelmshaven-Fort Mariensiel

The creation of the city of Wilhelmshaven can be traced back to the German-Danish conflict of 1848, during which the Danish navy blocked German shipping traffic. This led to the demand in Prussia and the North German Confederation for their own navy.
Image: http://de.wikipedia.org/wiki/Datei:2012-05-28_Fotoflug_Cuxhaven_Wilhelmshaven_DSC_3919.jpg
Location: 53.5130, 8.0456