OUTSIDE! Definitely!... So freeing and kinda wild... providing there isn't a blizzard or hurricane going on (though that actually would be pretty hot to fuck during a natural disaster!).
Definitely outside. Even in bad weather it can be fun. My idea of indoor sex, is doing it in a car! I love to have sex anywhere outside, beach, in the woods, by a stream, in a dark alleyway, in an open field or a park. Just about anywhere really.