Stockholm: the SL card covers the ferries, and the museums with free entry

An SL travel card or a tapped bank card covers metro, buses, trams, and the commuter ferries to Djurgården and the inner archipelago islands. Several state museums are free: the Swedish History Museum, the Medieval Museum, the Modern Museum's collection, and the Army Museum. The Vasa Museum (the salvaged 17th-century warship) charges and is worth every krona; go at opening. Skansen's open-air museum is the other must; it's a full day.