Summer Lovers (1982) on Netflix

Michael and Cathy, a young couple who have just graduated from college, have known each other about 10 years and have been together about half that time. They arrive on a nameless Greek island to spend two months for the summer of relaxing before going back to the real world. When they visit a nude beach crowded with other young tourists (a combination of American, British, French, German, Italian, Spanish, as well as Greek), they are hesitant at first but find themselves getting caught up in the uninhibited energy that surrounds them.