Explanation

 A 45.5metre (150-foot) deep diving pool with artificial underwater caves and Mayan ruins, the world`s deepest such structure, opened near Warsaw, Poland  in November 2020.

The complex, named Deepspot, even includes a small wreck for scuba and free divers to explore.
It has 8,000 cubic metres of water more than 20 times the amount in an ordinary 25-metre pool