One location is between Vouliagmeni and Varkisa, on the coast of the Saronic Gulf, about 25 km South of the centre of Athens. Vouliagmeni is a wealthy suburb of Athens, with a lot of private beaches and bars, and once you leave it following the coast road to Varkiza (also continuing further to Sounion Cape), it becomes completely deserted, not a single house. On this cape there are several rocky coves used for nude sunbathing and swimming. Swimming is good if you don't mind starting from the rocks (beware of your feet!).

My correspondent reports a few couples and more men in the nude (as is often the case).

One contributor says he wouldn't recommend this spot. It's fairly simple to scramble down from the lay-by onto the limestone / marble rocks, and there are flattish areas suited to lying or sitting. Most of these areas are out of sight of the coast road, although the traffic is still clearly audible. But getting into the water isn't at all easy - I didn't try it, and didn't see anyone else trying either. (At Alpha Limanaki, it's straightforward, and a waterside taverna takes advantage, creating a popular spot with no naturists in sight.) There were quite a few naturists around near Beta Limanaki - perhaps a dozen scattered around in singles and couples. All of them were male.

Another report says that the coves at Vouliagmeni and Varkiza are taken over from extremely early hours by Greek fishermen, which doesn't seem consistent with the earlier reports I have received; what's more the Saronic gulf is badly polluted. You have been warned.