Rungholt was a settlement in North Frisia, in what was then the Danish Duchy of Schleswig. The area today lies in Germany. Rungholt reportedly sank beneath the waves of the North Sea when a storm tide hit the coast on 15 or 16 January 1362.

The North Sea lies between Great Britain, Denmark, Norway, Germany, the Netherlands, Belgium and France. An epeiric sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian Sea in the north. It is more than 970 kilometres (600 mi) long and 580 kilometres (360 mi) wide, covering 570,000 square kilometres (220,000 sq mi).