An Italian spa complex has a swimming pool certified by the Guinness Book of Records as the world’s deepest. Named the Y-40 The Deep Joy, the pool is now the star attraction at the Hotel Millepini, located in the Montegrotto Terme resort area, near Venice.
The pool is filled with 1.1 million gallons (4.3 million liters) of thermal water from local springs, allowing divers to plunge without the skin suits they’d need in open seas or lakes. It also contains underwater caves aimed at training scuba divers to negotiate sub-aquatic landscapes. There’s also a suspended transparent viewing tunnel that allows spectators to watch the divers in action.