Yes, many many times.
The most thrilling probably at a recumbent stone circle site, which we visited as the sun set and light was failing.
We got to it against what appeared to be most conveniently placed stone that leant with enough angle to be used for supporting a fucking couple.
We were enjoying our sex in the semi darkness and as we did I could hear the odd noise now and again. Not put off, we continued until out the corner of my eye and coincided with a louder footstep noise on the dry grass, appeared a couple some yards away to our side.
Simultaneously I pulled out, cock wavering about in front of me and now fully in view of a low level torch light the guy was holding.
'We can see now why your lovely lady is making so much noise', the female said. The male then said 'Don't mind us, your in our regular spot, but we will go over there', as they passed us, to then start kissing and fondling each other.
'Oh right, thanks' I said, as we realised that they were as sexed up as we were. And we continued fucking.
Both of us now in competition with our sex noises as we both got to it.
A bit weird, but also turning into a thrilling and exciting session.