The site where Ft. Clinch now stands has been occupied since 1736 and it's easy to see why once you've taken in the view from atop its walls. Seated at the mouth of the St. Marys River and the Cumberland Sound, it's a perfect spot to mount a defensive campaign (not that anyone ever had to!)
Construction on the fort began in 1847 and the semi-completed fort was seized by Confederate troops in 1861. For a while it was a haven for Confederate blockade runners, as Amelia Island was the deepest harbor in the Americas at the time, thus a huge hub of illegal smuggling and whatnot. No sooner was the fort completed then technology rendered it obsolete, so Gen. Lee ordered it to be abandoned by the Confederates. The next year, Union troops took over the site, giving the north control of Georgia & Florida for the time being.
Today, what stands is an incredibly well-preserved site with barracks and walls you can walk all over. From the top, you can see north across the Cumberland Sound to Georgia's shores and south down Fernandina's beautiful stretch of uncrowded beaches.