Fort Sumter and Fort Moultrie National Historical Park

Fort Moultrie on Sullivan's Island consistently gets called the underrated local pick — free with a National Park pass, uncrowded, and covering 190 years of military history from the Revolutionary War through WWII, it often outshines Fort Sumter in locals' estimation. Fort Sumter draws the bigger crowds but carries a steep ~$40 ferry fee that the park pass does not cover, which turns off cost-conscious Charleston residents. Both sites are well-maintained NPS properties with knowledgeable rangers, but the consensus is that Fort Moultrie rewards those who seek it out, while Fort Sumter is the obligatory tourist stop.