Charlottenlund Fortress is a coastal fort by the Oresund, now better known as part of a beach and recreation area than as a military site. The grassy ramparts, pier, and narrow strip of sand make it a popular local place for swimming and summer lounging.
It is worth stopping if you are already in Charlottenlund or want a coastal walk north of Copenhagen. The fortress and nearby palace grounds give the area more character than a plain suburban beach.