The inland part of this small district is covered with lakes. The Großer Plöner See (Great Plön Lake, 29 km²) and the Selenter See (Lake Selent, 22 km²) are the largest lakes in Schleswig-Holstein. The lakeland and the adjoining parts of the neighbouring district Ostholstein constitute the region called Holstein Switzerland, since this is a very hilly countryside. However, the highest hill (Bungsberg) has only 168 m. North of the lakeland there is the Probstei, a region on the coast of the Baltic Sea.