World's deepest indoor swimming pool
The Nemo 33 diving pool in Belgium is, oddly enough, over 33 meters deep. It is filled with 2,500,000 liters of non-chlorinated, highly filtered spring water maintained at 30 °C (86 °F) and contains several simulated underwater caves at the 10 m depth level. There are numerous underwater windows that allow outside visitors to look into the pools at various depths.