My favorite lake to visit during the warmest months. It's located in the southwestern part of Berlin and it's reacheable by public transportation, just around 40min from the city center.
You can grab a coffee or a juice right next door to the KINDL Center in the old brewing Hall at König Otto, complete with all the fascinating brewing equipment from its completion in 1930 it is a hall reminiscent of German Expressionism style… or as stated on their website. :)
Tuesday's lunch hour tip is the amazing Berlin Philarmonic. A short-duration concert (around an hour) happens every Tuesday at 13h, for free. People make the Philarmonie's foyer full, sitting on the stairs, on the ground and everywhere around. Little advice: bring with you a little cushion for more comfort and try to arrive early to find the good spots.