Outside sex is the same mechanically as inside sex. Only your doing it under starry skies instead of a ceiling fan. (Warning: having sex in public is illegal. This post is for entertainment purposes only *cough*cough*)
Popular outside-sex areas:
*Woods behind highway rest stops
*public parks after dark (try it on the tire swings!)
*Cemeteries (always a favorite among goth highschoolers)
*Back yard (This is why the make privacy fences)
*Parking lots of abandoned stores
Just remember that having sex in public is like being a good ninja: Be quick, be quiet, and do it from behind.