Besides the feeling of being a hamster trapped in a wheel futility pumping my legs and not making any progress, there are other reasons I don't like the treadmill. You miss out on the natural breeze and fresh air of the outdoors, and the scenery changes as you move when outdoors. The best part about the nature trails around the Atlanta area is the wildlife. I've seen tons of squirrels, bunnies, been spooked by deer and spooked some myself (I even had one run with me for a few feet!), several Mallard pairs, and finally hawks. Specifically red-tailed hawks. Last Saturday I saw not one but two, and one was so close I felt like I was invading its personal space. They are very beautiful creatures and worthy of our respect. Surprises like this make running special each time I go out, which keeps me motivated.
Photo courtesy of http://www.ellenmichaelsphotos.com