Nemo 33 is a recreational diving center in Brussels, Belgium that is home to the world's deepest swimming pool. The pool itself consists of a submerged structure with flat platforms at various depth levels. The pool has two large flat-bottomed areas at depth levels of 5m (16 ft) and 10m (32 ft), and a large circular pit descending to a depth of 33m (108 ft). It is filled with 2,500,000 litres of non-chlorinated, highly filtered spring water maintained at 30°C (86°F) and contains several simulated underwater caves at the 10m depth level. There are numerous underwater windows that allow outside visitors to look into the pools at various depths.