The Georgia International Horse Park was the site of the cross-country race for the 1996 Olympics. This is still a very popular mountain biking trail, so just be aware when you head out.
The easier side of the trail winds through the woods and is a very moderate trail. The tougher side features some very cool sections of slickrock and some steep climbs and descents. This trail is unlike any other in Georgia!
From I-20, take Exit 82 "Georgia International Horse Park." Go North on 20 (or East on 138) for approximately 5 miles. There will be signs to turn right for the Horse Park. Large gravel parking area on the right. Pay $5 at the trailhead kiosk.
http://www.tripleblaze.com/trail.php?c=3&i=1293