Flughafensee

It's located right beneath Tegel Airport and you can watch the planes quite closely.

The lake is clean, the sand smooth and there are four beaches, the last of them occupied mostly by the weirdos, the beer-can-department and dogs.

"Fido sit", "Fido hold it", "Fido this", "Fido that", you can here conversations like this for hours.

You have to bring your own drinks and food, there's no place you can buy anything.