Middelgrundsfortet

Middelgrundsfortet is a sea fort located in the Øresund between Copenhagen and Malmö. It was constructed 1890–94 as a part of Copenhagen's sea-fortifications, partly from material excavated from Frihavnen. It is one of three artificial islands that were created to defend the entrance to Copenhagen's harbor. (The other two are Flakfortet and Trekroner Fort.)

Middelgrundsfortet was the largest sea fortress in the world, and is still the largest man-made island without abutment, with an area, including wave breakers, of approximately 70 000 m²; the buildings total approximately 15 000 m². A HAWK battery was placed on the island. Until 1984 the fortress was a military area; in 2002 it was sold to a private investor.

The fortress is constructed at a seabed 7 meter below the water surface, at the northern meeting point of the straits Kongedybet and Hollænderdybet.

Ferries connect Middelgrundsfortet with Langelinie, Copenhagen.