The incredible swim centre, designed by renowned architect Emanuele Boaretto, is located within the four-star Hotel Terme Millepini in Montegrotto Terme, Italy.
Operating since June, the pool has a diving height of a 12-storey building, or nine double decker buses placed on top of each other.
Wet suits aren't required here as swimmers can enjoy a regular temperature of between 32-34°C.
There is also a unique suspended underwater tunnel which is entirely transparent, so non-swimmers can experience the pool without getting wet.
There is a sunbathing deck with loungers on the roof, where swimmers can recover from their deep-diving experience.
Dry dock: The underwater tunnel runs right through the middle of the pool
Afraid of depths? The pool features several depth platforms before narrowing into a deep descent
Activities: As well as free diving, the pool offers opportunities for scuba divers to practice cave diving
Notable figures from Italian water sports helped to launch the facility this year, including Italian free diver Umberto Pelizzari, and Enzo Maiorca, the ‘father’ of freediving in Italy.
Freediver Ilaria Molinari even donned a mermaid tail to dive down to 40 metres to wow spectators.
'Y-40 is unique in its field thanks to the spa water, which cannot be outsourced,' says architect Emanuele Boaretto.
'We want to open up new medium and long term work prospects to try and guarantee prosperity, not only for my company but also for the surrounding land and society.'
Other-worldly: Free diver Ilaria Molinari dresses as a mermaid to swim through the artificial cave-diving area
Launch: Molinari dove the depths of the pool at its opening with the help of a mermaid's tail
The pool is situated in a regional natural park of the Euganean Hills in Italy.
Mr Boaretto is planning to cover the pool with lawn to b;lend the structure into its environment.
Y-40 is open all year round and offers the equivalent of diving the height of a 12-storey building.
Activities at the pool include scuba diving, free diving, aqua fitness, watsu, hydro-kinesi therapy and special activities for pregnant women.
The four-star hotel within the region of Villa Duodo boasts 100 air-conditioned rooms.
Architectural marvel: The pool is designed by renowned architect Emanuele Boaretto
The world’s largest swimming pool, completed in 2006, is located at the San Alfonso del Mar resort in Algarrobo, Chile.
It is estimated to have cost more than £613million to construct and covers nearly 20 acres.
Swimming a length in this would mean stroke after stroke for more than three fifths of a mile - that's 20 Olympic-size swimming pools.
The enormous man-made lagoon is set halfway up the country's Pacific coast and is filled with 66 million gallons of crystal clear seawater.
It uses a computer-controlled suction and filtration system to suck water in from the ocean at one end and pump it out at the other, while the sun warms it to 26C - nine degrees higher than the sea.
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