Walcheren is a former island in the province of Zeeland in the Netherlands at the mouth of the Scheldt estuary. It lies between the Oosterschelde in the north and the Westerschelde in the south and is roughly the shape of a rhombus. The two sides facing the North Sea consist of dunes; the rest of its coastline is made up of dykes. Middelburg lies at its centre; this city is the provincial capital and Vlissingen 9 km to the south is the main harbour.