Nemo 33 is the world’s deepest indoor swimming pool.The complex was designed in 2004 by Belgian diving expert John Beernaerts as a multi-purpose diving instruction, recreational, and film production facility.
The pool is located in Brussels, Belgium. Its maximum depth is 34.5 metres (113 ft). It contains 2.78787 million litres of non-chlorinated, highly filtered spring water maintained at 30 °C (86 °F) and holds several simulated underwater caves at the 10 metres (33 ft) depth level.
There are numerous underwater windows that allow outside visitors to look into the pools at various depths.