I live in Zurich, quite central. In summer, lots of people gather on the river bank (called the upper and lower Letten). Last dummer I went there with a friend, and before night fall I took off my swim wear and swam in the river naked. I think it would be a bit risky that people feel offended if I did this during full day, and someone might call the police. So I waited a bit, until people started leaving the place for dinner before I got into my natural attire.