An underwater house at Nemo, with the 34.5m deep pit in the background
The view down into the deep pit at Nemo 33
Nemo 33 held the record as the deepest indoor swimming pool in the world for ten years until the completion of Y-40 in Montegrotto Terme, Padua, Italy in 2014. The pool is located in Brussels, Belgium. Its maximum depth is 34.5 metres (113 ft). It contains 2,500,000 litres (550,000 imp gal; 660,000 US gal) of non-chlorinated, highly filtered spring water maintained at 30 °C (86 °F) by a solar heater and holds several simulated underwater caves at the 10 metres (33 ft) depth level. Due to the warm temperature in the pool, divers can dive for extended periods without a wet suit.  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 in 2004. A fee is required of the customers who use the pool. Popular Mechanics rates Nemo 33 as one of the top 18 strangest pools in the world.
The facility allows tourists, amateur divers, and professional divers. It requires that divers be 12 years of age or more and in good health. All divers must be either certified or supervised by a trainer. All divers must have a certified diver as a dive buddy.
The facility contains a restaurant, bookshop, swimwear store, souvenir store, and rooms for other water activities. It offers tours around the city of Brussels. Those who wish to use the facility can register throughout the year, including on holidays.