While the current structure dates from 1833, the origins of Vaxholm Fortress lie in 1544, when King Gustav Vasa ordered its construction to protect the Swedish capital and mainland. It repelled an attack by the Danes in 1612 and the Russians in 1719, among others. Inside, exhibition rooms explore the history of the complex and, more interestingly, the military's defence of the archipelago. From Vaxholm harbour, ferries to the island fort depart every 15 minutes from 10am to 9.45pm (return adult/child 40kr/free).