The Fort can be visited
Fort Louis

In the French Département Bas-Rhin, Fort Louis rises. The construction of Fort Louis was ordered in 1686 by King Louis XIV of France. From 1687, the fortress was built within ten years on an island in the Rhine, according to plans by Sébastien Le Prestre de Vauban and Jacques Tarade. Stones from the medieval Palatinate in Haguenau, which was demolished for this purpose, were used for its construction. The complex included two advanced bridgehead forts, Fort Alsace and Fort Marquisat, on the opposite banks of the Rhine. South of the main fort, the Fort Carré, the municipality of Fort-Louis simultaneously developed with a planned street network, whose settlement the king promoted.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://de.wikipedia.org/wiki/Datei:Vestiges_Fort_Carre_Fort-Louis_2006-1.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: 48.8067, 8.0608