The Fortress can be visited
Fortress Landau

The Fortress of Landau was a polygonal fortification in Landau in the Palatinate. Originally conceived as France's eastern outpost, it played a central role in the military conflicts of the 17th and 18th centuries, being besieged and conquered multiple times.
History+
After the Thirty Years' War and the Peace of Westphalia in 1648, the Imperial City of Landau came under French protection. With the Treaty of Rijswijk in 1697, the city was legally assigned to France. In 1688, King Louis XIV commissioned his fortress builder Marshal Vauban to transform Landau into a modern fortress. The old city walls were demolished, and within three years, from 1688 to 1691, the new complex with straight streets and squares was built. The Albersweiler Canal was constructed for material transport. In 1700, a crownwork was added on a northwestern hill.
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: 49.2034, 8.1064