Swimmers wanting to fetch something off the bottom of this pool will certainly need more than a lungful of air - seeing as it's a staggering 113 feet (34.5metres) deep. Located in Brussels in Belgium, Nemo 33, the world's deepest swimming pool, contains a whopping 660,500 gallons (2.5million litres) of non-chlorinated, highly filtered spring water that is kept at a temperature of 30C (86F). It takes the phrase 'being thrown in at the deep end' to a whole new level.