There is the main area, where there are all the big pools for the general public, like families with children. I think there are also some whirpools and spa-like facilities there, but no saunas.
And then there is the sauna areas, with pool, showers and relaxing spaces. There is the mixed one, it is bigger and has more saunas, one whirpool, one big pool outside and one small indoor pool. And the male part has like 3-4 saunas, one whirlpool outside and one small pool inside, as well as relaxing beds and stuff.
Everything was in german so it was hard to understand everything at the beginning.
In short, in other to get naked you have to pay the 13 extras. Also nudity is mandatory for the sauna but you can move around in a towel or in a robe. Most people don't do it though.