Vanilla and Rise and Fall
The Aquatics Center is the only building in the Water Park that requires additional research to build, and provides an impressive +2 Amenities to all cities within nine tiles of its district and +2 Tourism from all wonders on or adjacent to the coast. Building it in a city that's been used as a "wonder factory" will turn it into a tourist hotspot.
There's something to be said about the communal experience of enjoying the pleasure of water activities without the dangers of wild sea and lake creatures interrupting the fun.
Pools and aquatic centers have been a feature of cities for some time; take Pakistan's 'Great Bath,' one of the earliest known pools. Built sometime in 3000 BCE, it was likely a piece of religious construction (as indicated by the lack of slides and diving boards).
Contrast that modest 11.88 x 7.01 meter construction with the massive, 40 meter deep Y-40 pool in Italy (opened in 2014) and you can see the breadth and depth of the swimming experience.