Between the ages of 13 and 15 or so, outdoors was my favorite place to masturbate. Our house and lot were at the end of a country road, with a lot of trees and brush on our property. During the day, I often had an erection that just wouldn't go away (remember that age??), but until late at night, there wasn't any place in the house private enough for me to jerk off. So I would hide a few magazines and some tissues in a cloth bag with gardening tools (so that if anybody asked, I was going to weed the garden), and head up the hill to a copse of trees with lots of leaves and low branches.
There was a space between the trees just wide enough for me to hide in there. Through the leaves, I was able to see the house and road at the bottom of the hill, but be comfortably sure that no one could see me. And anyone approaching the trees from any direction would make enough noise that I'd have plenty of time to get decent and make up some excuse about being there.
I loved the feeling of taking my pants down while in those trees, feeling the breeze caress my butt, as I looked over whatever I'd brought. Even if I'd gone slightly softer during the climb up the hill, in no time at all, I was completely hard and erect again. I started tugging away while I looked at the photos (a lot of times, they depicted beautiful women getting stripped in forests or jungles.) I usually came in less than a minute, and the climaxes there were always especially good... I think because of the feeling of being outside, and also because I didn't have to worry about where my cum would go.
Sometimes before masturbating, I would wait with my pants down, looking out at what I could see from those trees. Neighbors' houses, people I knew and cars on the road were visible in the distance, and it was kind of a turn-on knowing that I could see them, but they couldn't see me (I hoped)... while I was nude everywhere it counts, on a guy.
Finally, I would wipe myself as best I could, pull up my pants, and carefully leave the copse from the back, working my way around to the garden and a little weed-digging, just to keep my cover story intact. I didn't even mind the work that much, with my cock wet inside my pants, while I was doing it.
My Dad complained a couple of times about how there were still too many weeds in the garden, but I don't think he knew why.