I may have mentioned that I enjoy all aspects of the great outdoors; and when I say "all", that does include having sex. I think it's fair to say I have a bit of an exhibitionist streak (all puns intended), and such activities do, irrespective of whether I'm actually being observed or not, feed that side of my personality.
The thing about about al fresco fornication is not that you are being observed, it's the fact that by doing out there in the open, there is the chance that you might be observed. I would go as far as to say that the "near miss" possibly gives more of an edge to the proceedings than actually being caught does.
I can only recall one instance where I can, with a reasonable degree of certainty, be certain that I was caught in the act. It was a particular warm, late summer/early autumn afternoon, we were walking through a forest trail somewhere in the Scottish Borders and the mood just came upon us. We left the reasonably well travelled path as struck deeper into the woods until we found what we thought was a suitably secluded spot and got down with getting down to it. The sun shone through the branches, insects buzzed, birds sang and we tried not to make too much noise as we enjoyed each other's attentions.
Perhaps we should have checked our location a bit more thoroughly before commencing because, while we were definitely out of sight of the path we left, it turned out there was another path nearby that we weren't quite as hidden from. As it happened, it was while I was in the process of getting my cock expertly sucked that I heard the dog bark and, as I looked up, I could see the back of its owner's head walking away from us. It didn't dampen our enthusiasm, however, so we continued until proceedings had run their course. It was only after we'd finished that we went to inspect the path that the dog-walker had been taken and, it was all to obvious that, unless they were blind or completely oblivious to their surroundings, they would definitely have had a clear view of us doing whatever we were doing at that time.
On the other side of this, there is only one occasion that I can recall where I have been the one catching the couple in flagrante delicto.
I was coming home late (around midnight) and had to pass through a couple of small closes to get from where the taxi had dropped me off and the street where I lived (the last 500 yards or such involved a convoluted one-way system that was quicker to walk, so I always got taxis to drop me at the nearby bus stop). The first close lead to a small, new build cul-de-sac, and it was there that I encountered them.
From what I could see, they were youngish, probably in their early 20s. I'm not sure if it was a last kiss goodnight that had gone too far but she had her back pressed up against the wall of (I assume) her front porch, her skirt up round her waist; while he had his jeans and boxers around his ankles and was fucking her with slow intensity that belied their quite clearly obvious location. Even if I hadn't walked past, anyone looking out of the windows of any of the houses on the cul-de-sac would have been unable to misconstrue what they were seeing. They were clearly enjoying themselves, lost in their own (far from) private moment and they gave no indication that they were aware of my presence. I didn't draw attention to myself and lingered only long enough to be sure that I was seeing what I though I was seeing before continuing on my way home.
These are both examples of unintentional voyeurism on the part of the viewer; the exhibitionism on the part of the couples involved (well, definitely on the part of the couple I was part of) was anything but unintentional. In our case it was a measured risk of what we were doing designed to heighten the arousal and enjoyment of the encounter.
There is, however, planned voyeurism. My only experiences of this, both as the observer and the observed have come through participation in swingers' clubs. Watching porn is one thing, but being right there in the room is something entirely different. There is an immediacy about it that is missing in porn. It's the fact that you are right there in the room with them; you could, if invited, reach out and touch them. The sounds you make in appreciation of what they are doing mingle with the sounds they make: the sighs, the groans, the collision of skin on skin. It is altogether a much more sensory experience than simply watching performers on screen. In front of you are "real" people" having "real" sex, not some stylised performance of over acting and asthmatic sound effects. The observer is part of the scene being observed and influences and participates in the scene just by being part of it.
I have watched, mesmerised and deeply aroused as two or more people have enjoyed each other's bodies, watched on by me and numerous others. I have been one of those bodies, both participating and performing, enjoying what we were doing to and with each other for our own benefit and the benifit of those watching, while also being aware of, and watching them watching us, and sensing their arousal from the scene in front of them.
It isn't for everyone, but for me, being in one of those rooms, as either an observer or an active participant, is a highly arousing and deeply erotic experience that few others come close to matching.
The times we currently lie in, do make me wonder if, rather than when, I will such experiences in those planned environments will happen again. As for the possibility of me being observed "in the wild", that only requires a willing partner, a reasonably seclude location and some suitably carnally clement weather for that to be a possibility.