Swan Creek Greenway National Recreation Trail, Exit 351, Athens, .3 miles off the highway.

Free. When you get off the highway turn on 72 in the direction of the Best Western and Applebees, not toward Waffle House. You'll cross a creek pretty soon, and the trail goes under that bridge, parking used to be on the right, but it may have been moved to the left, near the Winter Timber Outdoors store. It's a big name for a 2.3 mile trail, 4.6 round trip, but it is a nice, flat, mostly shaded trail beside a pretty creek. It is flat, flat, flat. Hiking, running, and biking. No horses as far as I know. Gas stations, restaurants, the works. Might as well go to Dub's Burgers while you are there, though you'll double the calories you lost. Classic, old style burger place. 

I can't find a link to a map, but there are map kiosks at the trailheads.