The oldest masonry fort in the continental United States, built by the Spanish between 1672 and 1695 to defend St. Augustine from British attack. Constructed of coquina — a compressed-shell limestone that absorbs rather than shatters under cannon fire — the fort was never taken by force. Live cannon firings on Saturdays. National Park Service site; inexpensive admission.
Castillo de San Marcos
Oldest masonry fort in the continental US, built by Spain in 1672