Fodor's Expert Review Castillo de San Marcos National Monument
The focal point of St. Augustine, this massive and commanding structure was completed by the Spaniards in 1695 (English pirates were handy with a torch back then), and it looks every day of its three centuries. The fort was constructed of coquina, a soft limestone made of broken shells and coral that, unexpectedly, could absorb the impact of British cannonballs. (Unlike solid stone, the softer coquina wouldn't shatter when hit by large munitions.) The fort was also used as a prison during the Revolutionary and Civil wars.
Park rangers provide an introductory narration, after which you're on your own to explore the moat, turrets, and 16-foot-thick walls. Garrison rooms depict the life of the era, and special cannon-firing demonstrations are held several times a day Friday through Sunday year-round. Children 15 and under are admitted free and must be accompanied by an adult. Save the receipt, since admission is valid for seven days.