Most Brit holidaymakers probably haven't heard about Suntago: Park of Poland

Despite being the biggest water park in the world, most Brit holidaymakers probably haven't heard about Suntago: Park of Poland.
Suntago: Park of Poland is about an hour's drive away from Warsaw.
The Treść niewidoczna dla osób niezalogowanych na forum. covers a whopping 75,000 square metres, and is divided into three distinct zones, Jamango, Relax Suntago, and Saunaria.
Across the entire water park, there are more than 35 water slides and 18 swimming pools, while the inside temperature never drops below 32C.

https://www.thesun.co.uk/travel/24502939/suntago-poland-biggest-indoor-water-park-europe/