Fredriksholm Fortress built
1662 CE.
Shown on the map at 58.095°, 7.982°.
Fredriksholm Fortress (Norwegian: Fredriksholm festning) was situated on an islet off Kristiansand, Norway. Today the former fortress is in ruins and the site is a popular place for sightseeing.
Text from the Wikipedia article Fredriksholm Fortress, licensed CC BY-SA 4.0.