The Fortress can be visited
Fortress Neuf-Brisach

The Fortress of Neuf-Brisach, an example of Baroque military architecture, is located in the French department of Bas-Rhin in the Grand Est region. This complex was conceived as the ideal form of a fortified city and is attributed to the strategic construction art of the 18th century.
History+
The need for a new border fortification on the Rhine arose after France had to return the fortified Breisach to Austria in 1697. Louis XIV then commissioned his fortress builder Vauban to construct a counter-fortress.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://www.n-tv.de
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Location: 48.0177, 7.5283