Nude bathing is an just an example of Freikörperkultur (literally, 'free body culture'), a movement devoted to the health aspects of being naked in light, air, and sun with the intentions to reform life and society. It exists even today under the term "naturism".
And who among us here can honestly say that they haven't gone 'skinny-dipping' or hot-tubbing sans swimsuits, whether with a person of the same or opposite sex, at least once in their lives?

-"BB"-