It's 33m deep and when people get to the bottom they'll find loads of cool passageways and rooms.
It was designed by diving expert John Beernaerts who wanted to create a space in Belgium for divers to use as there wasn't one there before.
Mr Beernaerts has also put in space for an underwater film set and hopes to see filming go on there soon.
It's taken seven years to get the pool made, and it also has space for scientific research.
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