Fort de Bertheaume
Plougonvelin, France
Fort de Bertheaume is a fort in Plougonvelin, in the Department of Finistère, France, in the cultural region of Brittany. It is located on a tidal island that nowadays connects to the mainland via a footbridge. The fort sits well above sea level, and its steep cliffs have rendered it easily defended for centuries. Since the 17th century, the fort's role has been to monitor the Goulet de Brest, the straits of Brest.
Fort data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).