I am a HUGE fan of public sex.
My fav was on the outside of the Stratosphere observation deck in Vegas. Also snuck off around a large boulder when we helicoptered into the Grand Canyon on a tour... with a few couples less than 100 yards away.
Seconded by a double couple blow jobs on the Texas Star. The day BigTex burned.
Cemeteries are also some of my favs... a picnic and playtime in the back where it's private...
A friend of mine has a rooftop patio that we fucked on in the rain...