In the southwest of Berlin lies the sprawling forest of Grunewald, with many unusual gems hidden amongst its trees: the Teufelsberg listening tower used by American spies during the Cold War, the Grunewaldturm, an 18th-century tower commemorating Wilhelm I, and Teufelssee, or “the devil’s lake,” a secluded nudist (FKK) lake. Many Berliners enjoy swimming and chilling on the lake’s floating platoon throughout the summer. It's easily accessible by public transport from Berlin and tends to not be as crowded as other inner-city lakes.