Stockholm

Stockholm needs 3 days: the Gamla Stan old town on one, the Vasa Museum (a 17th-century warship recovered almost intact) on another, and the Södermalm neighborhood on the third. May-September brings the best weather, with very long summer days due to the Nordic latitude. It's expensive, among Europe's priciest capitals. It's built across 14 islands connected by over 50 bridges, and its Vasa Museum displays a warship that sank on its maiden voyage in 1628 and stayed underwater for 333 years before being recovered almost complete.