The city is blessed with many beautiful parks, not least the Tiergarten, where people can enjoy summer sunshine without a stitch on, raising nary an eyebrow. The area around the Siegessäule is traditionally cruisy. There's also action around the Lowenbrucke (Lion Bridge). Biking is easy here as well, with designated paths to most everywhere. There's outdoor cruising at Friedrichshain's Volkspark around the Marchenbrunnen (water-fountain area), both day and night, but be cautious after dark.
The city has a network of public swimming pools with saunas, water cascades, and wave makers. In winter they provide a warm and cozy indoor retreat from the chill. In summer, open-air pools and lakes offer relief from hot weather. For pool info see Berlinerbaederbetriebe.de. For those interested in nudist-friendly spots, look for an "FKK" designation.
Badeschiff (Eichenstrasse 4), a floating pool on the Spree River in Treptow, is a gay-favorite on hot summer days, with bankside sauna, local bands and club nights form time to time.
Teufelssee, ‘Devil Lake’ in Grunewald forest, is easily reached on foot or by bike from Grunewald S-Bahn station, with clear waters for nude swimmers and lush lawns for sunbathers. The woods behind the parking lot are a popular men's cruising area. The nearby Teufelsberg offers great panoramic views of Berlin from a hill created with rubble from buildings destroyed in World War II. The heights are topped by a now ruined and deserted futuristic white dome - a US army radar installation during the Cold War.
The terminal of Templehof Airport was constructed in 1927 and enlarged by the Nazis in the mid-1930s - one of Europe's three iconic pre-war airports. During the Cold War closure of land and water access to the city by the Soviets, US and British aircraft of the Berlin Airlift flew supplies into the airport to sustain over two million residents for almost a year - among the greatest feats in aviation history. Operations ceased in 2008 and in 2010 the area became Berlin's largest city park. The terminal and the long tarmac runways remain open to visitors who walk, skate and bicycle the wide-open spaces. Numerous fairs and events also take place here. Platz der Luftbrücke U-Bahn station provides access to the site, named for the square, with a memorial to those who died during the Berlin Airlift.