The Fortress can be visited
Citadelle de Bayonne

The Citadel of Bayonne, named "Citadel General Georges-Bergé" on September 15, 1999, is a fortified work designed by Vauban in 1680 and built at the end of the 17th century, at the request of Louis XIV who wished to fortify the city of Bayonne.
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It is built north of the Adour on a hill overlooking the Saint-Esprit district. Since October 12, 1929, it has been listed as a historical monument of France. It is one of the 22 listed and/or classified monuments in Bayonne. The citadel comprises a square of 480 meters on each side with four large ear-shaped bastions, three half-moons, and tenaille in the curtain wall ditches to facilitate exits. Currently, the Adour Gate, known as the Royal Gate, is closed, its former guard post houses offices. The Emergency Gate on the north facade is now the only entrance.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://de.wikipedia.org/wiki/Datei:Bayonne_Caserne.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: 43.4986, -1.4733