St Simons Island is full of free things to do, you can visit on a budget or go for luxury.
This interesting National Park Service site is great on sunny or rainy days. Stop into the visitor center for a map.
There is a great maritime museum attached, and parks nearby too.
Several boat launches give access to the other barrier islands and the intracoastal waterway
Less than 5 hours drive from ATL, just over an hour from Jacksonville, St Simons Island is easy to get to