King Erik of Pomerania decided to take advantage of Helsingør's strategic position at the entrance to the narrow strip of water linking the North Sea and the Baltic. And so, in 1427 he introduced Sound Dues, a duty imposed on all passing ships, and built a fortress to enforce it. Largely rebuilt since that time, what is known as Elsinore Castle contains some outstanding rooms, including the Chapel, the King's and Queen's Chambers and the Ballroom, as well as the Danish Maritime Museum, which retraces a thousand years of maritime history. The fortress now listed by UNESCO as a world heritage site.