Hanko Fortress
Hanko, Finland
Hanko Fortress (Hangöbefästningarna in Swedish) was a fortress built in Hanko at the end of the 18th century, which consisted of the Gustavsvärn, Meijerfeldt and Gustaf Adolf fortresses built on rock outcrops, and the Kuningattarenvuori fortresses located on the mainland. The island fortresses formed a triangle that protected the sea channel leading to the port of Hanko.
Fort data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).