Located in Brussels, Belgium, Nemo 33 is currently the world’s deepest indoor swimming pool. Its “maximum depth is 34.5 metres (113 ft). It contains 2.5 million liters of non-chlorinated, highly filtered spring water maintained at 30C (86F) and holds several simulated underwater caves at the 10 meters (33 ft) depth level.” Continue reading for a video and more information.

There are numerous underwater windows that allow outside visitors to look into the pools at various depths. The complex was designed by Belgian diving expert John Beernaerts as a multi-purpose diving instruction, recreational, and film production facility, 2004.

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