The deepest pool is located in Brussels, Belgium. Named NEMO33, it is 108 ft. deep. It was built as a multi-purpose diving instruction, recreational, and film production facility. NEMO33 opened in 2004. The pool is 660,430 gallons of non-chlorinated, highly filtered spring water. The water is heated by solar panels to keep it warm - 86 degrees Fahrenheit. 

NEMO33 contains several simulated underwater caves at the 32-foot depth level. There are underwater windows that allow outside visitors to peer into the pools at different depths. At 16 ft. and 32 ft. the pool has two large basin areas and a large circular shaft. There are there are permanent bells of air under pressure where air is renewed constantly.