I had sex with my girlfriend on a clothing optional beach in Florida. The cliche thrill of getting caught was a turn on, but it also prevented us from enjoying it to the fullest. Supposedly there was an area where that kind of thing is tolerated, but it was to awkward to ask.
Then we tried out a field near this wooded area on my brother's property (he was away, we were house sitting). That was great, she led me to spot completely naked, like something out of a Femjoy shoot.
If we ever own property where we have privacy, I think I'd like to build a large, outdoor stone area where we could lay down some towels or soft mats when we want to "enjoy the great outdoors".
But I prefer indoors. My girl, baby oil and nature wouldn't mix.