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There is a small (15 meters) sandy beach on the left of freedom beach near Patong. Its a good places for nudity apparently.
Also near the Naithon beach is another small public beach with one restaurant. The owners accept nudity on the sunbeds & swimming, but not in the restaurant.
Ao Hin Lor has nice places for the enjoyment of nudity.
Wok Thum Beach. When you drive from Thong Sala the way to Wok Thum , after a small viewpoint restaurant you will see a big place without any building on the left. One the end of this place is a small path for go down to the beach, then you see a nice beach.
A small but nice beach is near Bovy Resort (Pirates Bar). But the watertide on this beaches goes down in the afternoon. Best time is morning and early afternoon.
A very small nice beach is near Freedom beach, however Thai ppl. like to go on the beach for picnics at the weekends.
Mind you, not everywhere is as welcoming