Fort Frederica is the most important historic site on St. Simons, and one of the most atmospheric Colonial-era ruins in the Southeast. The fort itself — built of tabby, a kind of concrete made from oyster shells, lime, and sand — is a low, half-tumbled fragment overlooking the Frederica River. Around it stretch the foundations of the planned colonial town that Oglethorpe laid out as an English garrison settlement.
The site sits in a grove of enormous live oaks draped with Spanish moss, which alone is worth the visit; bring time to walk the grass paths between the foundation stones of vanished houses. The visitor centre has a short film and a small archaeological collection. Admission is free with America the Beautiful pass; allow about two hours.