I haven't outside for some time now but have in the past. One of my favorite spots was on top of a rock on a hill. We would hike up the mountain and find a discreet spot, or at least as discreet as the open air can be. Obviously more dangerous in the daytime, but definitely more exciting. I am sure at some point someone in the surrounding houses must have seen.
Other spots have been: in a car, in a tent camping, backyard, and in a pool. Wow, looking back, I have had some FUN.