What does one do in Berlin when it's 104F, or 40C+? Well, we order ceiling fans. But when they arrive and our friendly handyman blows us off two days in a row, we look around, find a friendly pond, and drive on out. What a relief.
This pond/ lake wsn't terribly crowded (for Europe) because although free, it wasn't reachable by public transport.
(I'm posting this as per the date we went swimming, but I'm editing the post on August 18th and it's already difficult to remember what it was like being hot in Berlin, needing to pull out my shorts for the first time in three years, and wishing it were cooler.)