If it is open, Ft. Pulaski (operated by the National Park Service) is very interesting for those interested in American History in general, or the Civil War in particular.
Built to defend the Savannah River entrance from the ocean , the construction was under the direction of a new West Point graduate named Robert E. Lee. Equipped with cisterns for water, and with grounds for maintaining livestock for food, the fort is surrounded by a moat, and is designed for withstanding a siege.
At the outbreak of the Civil War the fort was seized from U.S. troops and became a Confederate fort.
It probably would have been able to withstand the bombardment of Union armies except for the fact that at the time of the attack on the fort, the Union forces were using
rifled cannon for one of the first times. The rifled cannon had a longer accurate range than the defending smooth bore cannon in the fort, so the Union forces simply sat out of range and demolished the forts' defenses.
I recommend visiting the fort. However, the NPS website for the fort says it is temporarily closed due to severe weather conditions. I'm sure you can inquire about it being open just before you go.
Fort Pulaski National Monument (U.S. National Park Service)