I like this too. One time I went out at the dead of night at around 2.00am in the morning, it was pitch black and fairly chilly. There is a large area of woodland with huge trees, it is very secluded and lonely. I used to get at the top of a hill in secluded trees and then strip naked and roll all the way down the hill slipping and sliding through thick mud and sludge all the way to the bottom. I used to try and climb back up the hill naked and it was a turn-on when I couldnt because it was so slippery and muddy and I would just end up back where I started, flat on my belly and covered head to toe in mud.
I really enjoyed being exposed in the outside. I could feel the wind against my skin and just being nude in mud was mind-blowing.