Originally Posted by petervik

The short answer is: yes, it's entirely normal. At any sauna in Germany, whether public or private, you are expected to be naked. It is socially unacceptable to wear swimming trunks or to fail to sit on a towel. The majority of saunas at hotels or public swimming pools are mixed gender. It is simply not a social issue in Germany, where work colleagues, neighbours, students, grandparents, parents and children of both genders find it perfectly natural and without problem to be naked together. The same applies in Austria and to some extent in the Netherlands and parts of Scandinavia.

The implication behind your post was that the Germans were wrong to expect to you conform to German rules, practices and social norms. We all need some sensitivity when travelling in different cultures. If you find nudity offensive, don't visit German saunas and swimming pools - or beaches and lakes. Or indeed Germany and such countries.