Fort Frederica National Monument at the north end of the island is the main historic attraction — ruins of the 1736 British colonial fort and town, beautifully set among massive live oaks. The St. Simons Lighthouse at the south end is also open for tours and worth the climb for the views.
The island has good beaches on its eastern shore, though they're not the wide, sandy expanse of resort beaches — more natural and low-key. Neptune Park near the village pier has a pool and green space. Biking is a pleasant way to get around; rentals are available in the village.
The surrounding salt marshes and tidal creeks are excellent for kayaking. Several outfitters in the area offer guided tours. Fishing — from the pier, from the shore, or on a charter boat — is popular year-round. Crabbing from the shoreline with a simple chicken-on-a-string rig is a classic local activity that works surprisingly well and keeps everyone entertained.