I've had sex in a lot of public spots, but this one was the most out there for me:
Freshman year of college, I was a pent-up little freak. Found a guy with a big dick on the internet somewhere. He lived with his parents at the time and I lived with mine. So I had him meet me in the parking lot and I took him to the very edge of the campus. Over the fence was a railroad track and then immediately past the tracks was some kind of an industrial area with warehouses and trucks. The fence was completely see-through.
I had him fuck me on the grass right next to the fence -- in broad daylight, on a weekday. I'm sure there were students walking around nearby but neither of us cared much. I tried not to scream too loud but you know how it goes when your pussy is just getting used to getting pummeled by a big dick, and I'm pretty sure that some of the warehouse workers and truckers either saw or heard us.