no real berliner goes to the swimming pool, as berlin is surrounded by numerous lakes on all sides. stressed urbanites need approximately an hour to reach the lakes by public transport. the best is wannsee. the wannsee is a famous open-air lido though, that is usually crowded with people. even in the midst of the holiday season, it is possible to find a quiet place at the more remote lake corners. If you want to have a more action packed experience, try to stop one of the many boat owners and blag for a ride around the lake. most will be happy to show off their pride and joy.