Tired of the treadmill at the gym, or the sidewalks of your own neighborhood? Why not challenge yourself to a hike out in the middle of nowhere? Take yourself to some out-of-the way forest or park and get going.
Set aside a morning or afternoon, get a trail map at a local store or park information center, and follow a trail. Or just walk along a backwoods road, one that's rarely traveled. Walk on the side facing traffic, of course. Even better, you can bring a friend to share the experience with you.
You could go on a wildflower or bird watching hike, or challenge yourself by climbing up a hill or mountain. You could explore a cave, or check out a hidden mountain waterfall or stream, accessible only by foot. The staffs of state and national parks know the ins and outs of their territories and love to introduce new people to them. So don't be shy about asking for advice.