Even though old buildings and barns aren't really "nature" subjects, they appeal to me as an outdoor photographer because in many ways they provide similar experiences as when pursuing other outdoor images. I can photograph old buildings in natural light and a lot of times it's the atmosphere and composition of the surrounding landscape that motivates me.
The elements of nature making their mark on the subject blur the boundary between man-made and natural, whether it's foliage that has grown over (or through) an old house or years of rain and snow that has etched worn colors into barn wood.
Of course, there's always the human interest in wondering: Who built this structure? Who used it? Where are they now? These questions make photographing old places and their details intriguing and a little mysterious.