Karlskrona is Sweden's major naval port and a good example of a planned town of the 17th and 18th centuries. The WH site covers several buildings in the city itself and on the islands nearby. The major attraction is the huge Kungsholmen Fortress, which is still today operated by the Navy, so you need a special permit to visit. The tours on the day of my visit were already full, so I could only do a harbour cruise that stopped at the island but did not include a visit. There is still quite a bit to see from the outside, though, and it is certainly an impressive sight. A pleasant stroll through the city takes you to several historic sights, including churches (the Admiralty Church is the largest wooden church in Sweden), squares, fortresses and other military installations. Everything here is quite nice and well-maintained, and you can easily spend an enjoyable day in Karlskrona. Don't forget to visit the Maritime Museum, though - this is really a first-class sight.