A Summer Day in Germany: Stunning View of the Ruppiner See Discovering Ruppiner See Ruppiner See, stretching 14 kilometers in length, is the longest lake in the state of Brandenburg. With a maximum width of 800 meters and a depth reaching approximately 24 meters, it is a natural marvel. The lake is bordered by several towns including Neuruppin, Alt Ruppin, Gildenhall, Gnewikow, Seehof, Karwe, Wustrau, and Altfriesack. Neuruppin, the district town of Ostprignitz-Ruppin, is .