Kennesaw Mountain National Battlefield Park, located on exit 116 on I-75, offers some
great running trails, some of which are quite challenging. The trails are well-maintained
but quite hilly. You can knock out long runs in the shade of forest scenery.
The Chattahoochee River trail system is another great set of trails. Although there are several park locations in Atlanta, the best location for Trail running is the Cochran Shoals unit, just off I-285 at the Powers Ferry/Northside Drive exit. The park provides ample parking, and its popular, manicured trail has a slowly-climbing offshoot that leads to another park station (about 30 minutes away if running a 7-min pace).
NOTE: there are two parking lots for the Cochran Shoals location, but the more populated lot is the second one, which features the clearly marked, flat 3.1 mile loop and the fun offshoot. If you use the first parking lot off of I-285, you'll be running narrower, less popular trails that can get snaky during the summer. Also, the trails from the first parking lot don't go as far.
How to run the fun part of the trail:
If you start from the popular Cochran Shoals parking lot, you can run a mile or so until you see the offshoot trail climbing up into the woods. Take this trail, explore the trails around the other park station (Paper Mill unit, where the trail ends) and head back to the Cochran Shoals parking lot for a total of 10 or more miles. The trails are quite popular and safe, although you'll need to watch out for mountain bikes if you run at one of the popular times (Thursday evenings, Friday, Saturday or Sunday). By the way, there's a two-dollar parking fee.
Directions to park:
From I-285, head to the Powers Ferry/New Northside Drive exit (on 285E, first exit after the 75/285 junction merger). Exit to the right, then take a left onto Interstate North parkway. The first parking lot will be on your right, but don't park here unless it's rush hour and the other lot is full. Instead, drive across the bridge to the second parking lot, which will be on your immediate right.