The complex, named Deepspot, includes a diving pool with artificial underwater caves and Mayan ruins - and even a small wreck for scuba and free divers to explore.
Unlike regular swimming pools, Deepspot can open despite corona-virus restrictions in Poland because it qualifies as a training centre because it offers courses.
Deepspot is located in Mszczonow, a town in central Poland, about 40 kilometers away from the Polish capital Warsaw. Construction began in mid-2018.
"There is no beautiful fish or coral reefs here, so it is not a substitute for the sea, but it is really a good place to learn and train in order to dive safely," Przemyslaw Kacprzak, a 39-year-old scuba instructor who was among those attending the swimming pool's opening, told EuroNews.
Construction took two years and cost 40 million zlotys (€8.9 million). Currently it is the deepest such pool, surpassing Montegrotto Terme in Italy which is 42 metres deep. The Blue Abyss pool planned to open in Britain in 2021 will be 50 metres deep.