At the end of the Baltic Sea arm Schlei, which idyllically stretches between the hilly landscapes of Angeln and Schwansen into the Schleswig-Holstein mainland, lies the town of Schleswig with its 25,000 inhabitants. Schleswig is probably one of the most historically interesting cities in the state between the North Sea and the Baltic Sea. This significance becomes most apparent during a visit to Gottorf Castle, which is part of Schleswig's urban area and is impressive for its sheer size. The large building, which today serves as a museum and archive, is considered to be a testimony in stone to the many centuries of opposition and cooperation between Danish royal power and regional dynasties. In addition, Schleswig has a lot to offer with its old town, a lively cultural and water sports scene, the impressive cathedral directly on the Schlei River, and the nearby Viking village of Haithabu.