Three (1969)
Sort of a 'Summer Lovers for the 1960's, Three finds two college friends, traveling in Europe, finding themselves rivals for the attentions of a mysterious woman. The two friends are played by Sam Waterston and the equally appealing Australian actor Robie Porter. The beautiful woman, the beautiful Charlotte Rampling.
Written by Irwin Shaw based on his own short story, 'Then We Were Three', Waterston play Taylor an appealing and caring young guy, who sadly ends up being the third wheel in the triangle. I believe this to be Sam's only nude scene other than in the film Sweet William. The story in Three is both compelling and a little sad, but the location scenery makes for enjoyable viewing. I couldn't find a copy anywhere, but someone thankfully someone put the entire flick on YouTube which you can find HERE: The clip of Sam's naked dive into the ocean, I added below.