In the back garden ... in the middle of the day...2 weeks back! , (and no we don't have a huge back garden and yes, it easilly overlooked by the neighbours(who don't have kids so dont fret about kiddies seeing what they shouldn't)
Also on the beach
In the woods
on the loo (yes it has icky connotations but it worked for us)
on the steps
I am usually the one who initiates any outdoors hankypanky but somehow my husband never seems to complain :-)...keeps it spicy after 13 years...!