Großer Segeberger See

Within the lakes of East Holstein the Great Segeberger See is characterized by a special history.
After a salt dome with gypsum or anhydrite rock had risen due to salt tectonics to near surface, was released after thawing the glacial permafrost groundwater gradually dissolve rock salt and gypsum in the subsurface and leach underground cavities (subrosion). The overlying layers of rock and debris sagged, leaving sinks filled with water. This formed u.a. several lake basins, which were initially covered by a contiguous water surface. After a possibly due to a fall event in later time natural lake level drop, the original waters divided into the Great Segeberger See and the northeast located much smaller Klüthsee.
The Great Segeberger See is part of the gypsum karst landscape of Bad Segeberg and thus stands in a context of origin to Kalkberg and its cave
Source: Wikipedia

Wonderful way in every season

The 8 km long tour begins at the beginning of the lakeside promenade at the Jahn monument. From this point you have not only a magnificent view over the beautifully situated Großer Segeberger See, but also on the 89 m high wooded Kagelsberg, the 81m high Moosberg and the houses of Stipsdorf. The lake has a size of 178 ha, a length of 2.6 km and measures at its deepest point 12 m. The city of Bad Segeberg is the owner, but has leased it to the Segeberger Sportfischerverein. On the water of this lake operate seven clubs their water sports. Motorboats are not allowed on the lake.
Source and other interesting information:
segeberg.info/sp_103-rundgang-grosser-segeberger-see-sta.htm

Unfortunately, the route around the lake is totally overcrowded in good weather. Especially in the area of ​​the city.