Another vote for the Phönixbad in
Ottobrunn - it has 2 extremely shallow play pools, a learning pool with very warm water, an "adventure" pool half indoors and half outdoors, also with warm water; the "adventure" pool also has a waterfall, loungers in the water with massage jets, and a big curly slide.
And, for people like Kat, there is also a "proper" pool with cooler water for doing "serious swimming", as well a separate diving pool, jacuzzi and sauna, like Austrami said.
Great place to go in all weathers - plenty of space outside, as well as free loungers and sunshades!