While it helps to kill off bacteria, it also serves as a subtle reminder that you are wading around in chemically treated water (if tasting the odd mouthful just isn't enough). Switzerland's Naturbad Riehen swimming pool is entirely chemical-free, relying instead on a biological filter system to provide clean and natural water for thousands of patrons, no itchy red eyes in sight.

A town of around 20,000 people, Riehen sits just outside of Basel on the Swiss-German border. This section of the border wraps around Riehen in such a way that in 2006, the town's old swimming pool had to be demolished to make way for a tunnel connecting two German cities on either side. With the controversial roadway completed in 2013, the people of Riehen were quick to reclaim their territory.