Play in or watch a community soccer game
The just-opened Station Soccer is the first public soccer field located in a public transportation station anywhere in the world. It's at Five Points MARTA Station, which eventually you'll probably have to pass taking the train to the airport, unless you're already south of it. If you're driving, just park your car at a MARTA station that offers free parking (West End is just two stops south of Five Points, FYI), then catch a 5-min ride north, and you can hang for a while, before getting back to your car with time to spare. You'll not only retain your sanity by taking MARTA (Atlanta traffic is pure evil), but you also might meet some new friends to kick it with the next time you’re in downtown ATL.
Time: 40 mins of watching/playing, 10 mins each way navigating MARTA stations