On a peninsula near the mouth of the St. Johns River, Yellow Bluff Fort Historic State Park protects a slice of Florida history from the War Between the States.
Resources

Overview
Location: Jacksonville
Lat-Lon: 30.399837,-81.555634
Fees: Free
Open: 8 AM to sunset daily
Location
Details
Earthworks – mounds built as fortifications for soldiers to fire from and duck behind – were constructed here in 1862 by Confederate forces to maintain control of this critical river route.
After defeat by Union raiders, the site became an encampment for Federal troops, with more than 250 soldiers stationed here to watch over access to the river.