Stop 1
Castillo de San Marcos
The coquina fortress on the bayfront · about 15 min here
Begun in 1672 and finished in 1695, the Castillo is the oldest masonry fort still standing in the continental United States. Its walls are coquina — shell-and-limestone rock quarried on nearby Anastasia Island — which compresses instead of shattering when struck by cannon fire. The fort changed flags repeatedly (Spain, Britain, Spain, the United States) but was never taken by force.
Look for
Stand at the moat wall and look for the diamond-shaped bastions at each corner, and the shell fragments visible in the stone.
Walk to the next stop
Walk south along the seawall path, then cross Castillo Drive at the crosswalk toward the two stone pillars.