Eemshaven, Delfzijl (NL)

Wikipedia says “Mudflat hiking (Dutch: Wadlopen) is a recreation enjoyed by Dutch, Germans, Danes and others in the Netherlands, northwest Germany and in Denmark. Mudflat hikers are people who, with the aid of a tide table, use a period of low water to walk and wade on the watershed of the mudflats, especially from the Frisian mainland coast to the Frisian islands”.