I went scuba diving in the Great Barrier Reef and thought that my 7-meter adventure was the most daring thing I had ever done. But one thing’s for sure, I’m never, ever going to step into the Nemo 33. This 33-meter deep swimming pool is filled with specially filtered un-chlorinated spring water. It is built with simulated caves, several platforms and a 33-meter deep cylindrical pit; that’s deeper than you are allowed to go on a standard scuba diving license. The Nemo 33 requires 2,500,000 liters of water to fill it and the temperature is maintained throughout the pool and is located near Brussels, Belgium.