To be privately owned
Fort IV (Köln)

Fort IV in Cologne, once known as “Erbgroßherzog Paul von Mecklenburg,” is an example of 19th-century Prussian fortress architecture. Originally built as part of Cologne's city fortifications, it underwent a transformation and now serves a versatile use.
History+
The construction of Fort IV took place between 1822 and 1825. The plans originated from the Oberbaudeputation in Berlin, led by Schinkel, while the construction was supervised by Jachnik, Elsner, and Buschius. The fort underwent a transformation between 1887 and 1889, when it was converted into a ruin, designed by Adolf Kowallek, integrated into the Volksgarten. Stair towers were also added during this period. At that time, it housed a restaurant, which occasionally served sparkling beverages. Later, from 1930, the local Red Cross branch used the fort as a first-aid post.
Source: Wikipedia · Licence: CC BY-SA 4.0
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: 50.9223, 6.9437