Two memorable times outdoors: Once in the woods of an elementary school playground (while youngsters were on the swings within shouting distance--yikes!)... I laid down on my stomach on the dirt path, ktspktsp flipped up my skirt, and away we went. Hot hot hot.
Second time was last summer, after hiking to a 2,400 ft (800 meter) peak in Iceland on the most beautiful day of the year. We parked ourselves on a very open hillside (it was a long mountain, more like a range), with a nice view of Reykjavik below us, and away we went... right there in the open air. It was fucking awesome. The only downside is that ktspktsp lost his watch there, which was a very nice one that was given as a wedding gift from his parents... oops.
We even hiked back up to look for it, several times, but apparently someone took it as an Outdoor Sex Toll, who knows. But still, it was fucking awesome.