Kastellet
Kastellet — or “The Citadel” in English — is a star fortress located in Copenhagen, Denmark. It was built in October 1664 as part of a continuous ring of star forts surrounding the city, and it remains one of the best-preserved ramparts of its kind in Northern Europe. Kastellet still houses some Danish military operations today, though it primarily serves as a public park and historic site.
55.691417°, 12.595528°