Kastellet in Copenhagen was constructed in 1663 under King Frederik III, after the original fort on the site was compromised by a Swedish attack in 1658. It was partially rebuilt again in the nineteenth century when the distinctively star-shaped building, flanked by a moat, served as a prison.
During the Second World War, Kastellet was used as a base by German forces whilst they occupied Copenhagen.
Today, still in a great state of preservation, Kastellet is a military base. Its grounds have been turned into a park, which is open to the public, although there is no access to the inside of the fortification.