Fort Clonque
Alderney, Guernsey
Fort Clonque is a 19th-century coastal fortress in Alderney, in the Bailiwick of Guernsey in the Channel Islands built on a rocky outcrop of land joined to the island by a causeway that can be submerged at high tide. It was constructed at a time when French naval power was becoming an increasing concern to the British. It was manned by fifty-five men and fortified with up to ten guns, mostly 68-pounders; however, none were ever fired in anger.
Fort data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).