The Great Plön Lake is the largest lake in Schleswig-Holstein, a broad sheet of water of some thirty square kilometres, dotted with islands and fringed with reed and woods. It lies in the middle of the Holstein Switzerland lake district, where the retreat of the ice sheet some fifteen thousand years ago left a landscape of hollows, ridges and dozens of lakes, large and small. The town of Plön sits on a narrow neck of land between the big lake and the smaller ones, and as a result you rarely lose sight of water anywhere in it.
The lake is an important site for wildlife. Reed beds hold great crested grebes, herons and warblers, white-tailed eagles hunt over the water, and in winter large flocks of ducks and geese gather on the open areas. A research institute for evolutionary biology, run by the Max Planck Society, has been based in the town for decades, and it studies the plants and animals of the lakes, among other things. There is something pleasing about a place where scientists spend their days measuring sticklebacks and mice within sight of a castle.
On a bike, the lake roads here are some of the best in the north. They curl around bays and headlands, climb the low moraine hills and drop through beech woods, with glimpses of water and sky at every turn. The bends are smooth and open, the surface mostly good, and the traffic light enough that you can settle into a rhythm. On a still, bright morning, with mist on the water and the sun low, it is a lovely way to spend an hour. Summer weekends bring cyclists, caravans and lakeside crowds, so avoid peak afternoons if you can.
Plön is a town of about thirteen thousand, with fuel stations, supermarkets, bakeries and cafés, so there is no need to plan anything special. The lakeside promenade is a nice place for a stroll and a coffee, with views over the water and the ducks to keep you company. If you want to see more of the lake, small passenger boats run in the season, and you can rent rowing boats at several places. Be careful of the wind on the open water, which can get up quickly. Autumn, when the beeches turn gold and the reeds are tawny, may be the best season of all.