Nemo 33

Nemo 33 is an indoor non-chlorinated fresh water facility in Brussels, Belgium.

It previously held the Guinness World Record as the deepest indoor swimming pool in the world between its opening on 1 May 2004, and the completion of "Y-40 The Deep Joy" at Hotel Terme Millepini in Montegrotto Terme, Padua, Italy, on 5 June 2014.

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 dry suit.

[1] Popular Mechanics rates Nemo 33 as one of the top eighteen strangest pools in the world.

An underwater house at Nemo, with the 34.5 m deep pit in the background
The view down into the deep pit at Nemo 33