Social nudism has me totally spoiled on taking showers outdoors. I'm not sure I can describe the appeal any better than that of just being naked outdoors, or skinny dipping - it's more than just some exhibitionist thrill (although, as a voyeur, I will say that a person with an attractive body rubbing themselves down in the shower - especially surrounded by nature - is one of the great aesthetic pleasures in this life, and I wish there were more opportunities to witness it); it's a primal sensation, of being naked among the elements, with the addition of water providing another tactile dimension. I'd love to stand naked under a waterfall someday.
P.S. The best way to dry off is not with a towel, but open air and sunshine. -_^