Have something to lie on, the pebbles are quite large. An hour's walk from Paleohora, fine pebble beach. Lissos Tiny pebble beach. Used to be pretty deserted. Sougia Sougia has a long pebble beach.
Nudism is usual towards the eastern end of the beach.
Now of course, more people have boats so you are not always alone. I think that someone in Loutro even organizes a weekly excursion by boat. Go and have a look. Here again, do not mess up a piece of undisturbed nature by leaving any rubbish. As I wrote earlier, it is possible to walk to it but do not attempt it without a guide.