Located in Brussels, Belgium, Nemo 33 is the deepest indoor swimming pool on Earth. With two large flat-bottomed areas reaching depths of 5m (16 ft) and 10m (32 ft), a number of underwater side rooms, and an incredible circular pit plunging to a distance of 33m (108 ft), it looks like a Disneyland for swimmers and divers. Moreover, if you’re afraid of taking a deep dive, numerous underwater windows allow outside visitors to look into the pool at various depth levels.