I am a mature student and therefore a lot older than the previous posters.
I have had saunas and used steam rooms in Germany and the Netherlands, and visited one in north London, all where no-one wears swimwear and sits on a towel or with one wrapped round. The one in north London describes itself as naturist, although I don't consider myself as one. In Germany and the Netherlands, at the places I have been to usually about 55-60% of the visitors are women, which is different from the UK where it is about 80%-90% men. A sauna without swimwear is way more comfortable.
I have been to clothes optional beaches in the south of France. Nice to be able to change and not have wet swimwear or have to do the towel dance, just need to always remember suncream of a high factor.
No wish to ever do the World Naked Bike Ride. I think it has lost much of its original purpose as a protest against car dependency.