Opened in the summer of 2004, the facilities have proved highly popular as it has allowed Berliners to swim (at least in a figurative sense), in the long polluted and unsanitary Spree. In fact on closer inspection you can see several people swimming when this image was captured.

The 32 metre-long pool also has a bar with DJs until midnight, and is even open all-year-round.

Read more at Wikipedia.

Thanks to Jake.