People look at the Harmony of the Seas cruise ship leaving the STX shipyard of Saint-Nazaire, western France, for a three-day test offshore, on March 10, 2016. With a capacity of 6.296 passengers and 2.384 crew members, the Harmony of the Seas, built by STX France for the Royal Caribbean International, is the world's largest ship cruise. (Photo by Loic Venance/AFP Photo)

Swimmers in fancy costume take part in the New Year's Day swim at Saundersfoot in Wales, Britain, January 1, 2017. (Photo by Rebecca Naden/Reuters)

In an observance of Epiphany, Russian Orthodox believers swim in an icy pond outside Nizhny Novgorod, Russia. (Photo by Olga “Zwezdochka”)

Coffins are lined up near the wreckage of the bus, on July 29, 2013. (Photo by Salvatore Laporta/Associated Press)

The Bondi Icerbergs Pool was converted into a giant esky ice chest during the filiming of a Jim Beam commercial at Bondi Icebergs on March 21, 2013 in Sydney, Australia. (Photo by Marianna Massey)

To mark Halloween, 150 teens descended upon a swimming pool in Essex to help mobile network giffgaff recreate the famous Tomatina tomato fight... only this time, with blood and guts. Different takes #giffgaffguts. On October 18, 2013 in Dagenham, England. (Photo by Dave J. Hogan/Stringer for giffgaff)

The Y-40 Deep Joy is the worlds deepest pool. Y-40 is projected by Architect Emanuele Boaretto and supported by the “Boaretto Group Hotel and Resort”. The name Y-40 is inspired by mathematical symbols. “Y” is the ordinate axis of the Cartesian system and “–40” means the world's record depth or our pool- that is 40 meters underground. (Photo by Courtesy Y40 Deep Joy)