The Chattahoochee River National Recreation Area is a fun place around metro Atlanta despite the pollution in the river. I wouldn’t recommend rafting in the river now (I did it countless times in the distant past), but there are some nice short hikes there.
Here is the track log of the East Palisades loop trail in GPX format.
You can also get park maps in PDF format.
Below you can see the trail we followed as well as some photographs. Since we hiked there in early November, you can see some nice fall colors.