Ship's Island (Skeppsholmen) used to be the Naval Base for more than four centuries including shipbuilding and docks. This all ended in 1969 when the base moved into the archipelago. I myself did most of my conscription service here and worked in the small pink castle like building with cute turrets. That used to be the HQ. Now the island is known for its museums (Modern, Architecture, East Asiatic) and a popular hostel in an old sailing ship (Chapman). It's good for strolling and has a number of old boats at its quays with interesting information on plaques.