Located in Brussels, Belgium, Nemo 33 is the deepest indoor swimming pool in the world. The 113 feet deep pool contains 2.5 million liters of water, about the same as an Olympic-sized pool. The water is maintained at 86 °F and there are plenty of simulated caves to explore. The pool is open to tourists and amateur and professional divers as long as they are at least 12 years old and certified or supervised by certified trainers. There is also a restaurant at the facility so you can enjoy one last meal before having a panic attack at the bottom of the pool.