A while back there was a young lady I was seeing who always got excited when we talked of strangers watching her/us, but never planned anything.
We always enjoyed having her strip where she could possibly be seen.
One time we were in waterfront park. She had been wearing a thin top with no bra that you could see right through, and we passed several people before we found what we thought was a seclued spot away from everyone by the water.
She loved to get me going, so she slid out of her clothes right there and leaned against a tree that hung over the water. Of course it wasnt long before i had her breasts in my hands. As I was sucking each of her nipples, something caught my attention on the other side of the tree, and sure enough it was a guy standing there watching.
He was trying to be discreet & act like he was just looking at the water, but couldnt stop staring at us. She hadnt seen him yet as she was caught up in our foreplay, but I stopped sucking her nipples for a moment, and just nodded a "yes" to him so he knew it was ok to watch.
She saw him & realized what I had just told him, and without saying a word we went back to focusing on each other.
She got on her knees and sucked my cock while I positioned us so he had a great view. We had brought a blanket and for how long I couldnt tell but we fucked in every position while he watched. I had her riding and positioned so she was facing him. She told me later she could see he had his cock out stroking away, and that she came several times while looking at him while he watched her riding.
I pulled out of her when I came and she quickly took my cock and swallowed every drop. We both dropped down on the blanket to catch our breath, and when we looked over he was gone.
No idea who he was, and I'm pretty sure he didnt take any pics (his loss) but it was a great experience for us