Castillo de San Marcos

The Spanish crown's coquina fortress guarding Matanzas Bay, built 1672–1695 to defend St. Augustine and still the oldest masonry fortification in the continental United States — and the only one built entirely of coquina, the local shellstone quarried across the bay at what is now Anastasia State Park. The soft stone absorbed cannonballs instead of shattering, and the fort was never taken by force in three centuries of siege. Self-guided access covers the moat, gun deck, chapel, powder magazine, and living quarters; costumed rangers fire replica cannons from the gun deck Fridays, Saturdays, and Sundays. Run by the National Park Service. Adults $15, kids 15 and under free.

What to order

Walk the gun deck first for the harbor view, then time the visit around a cannon firing (Fri–Sun, five per day). The fort lot fills by mid-morning — park downtown and walk the seawall in if you arrive after 10a.

Hours

Daily 9a–5:15p (last admission 5p) · closed Thanksgiving and Christmas