Fort Matanzas National Monument, Florida

The city of St. Augustine in northeastern Florida is among the oldest settlements in America. And just a short drive away, you can take a free ferry to see little-known Fort Matanzas, built by the Spanish in 1740 to protect the city.

The small fort is on an island in the mouth of the Matanzas inlet. Look closely and you'll see the fort is made of coquina, soft limestone formed eons ago from millions of tiny clamshells. During a 45-minute guided tour, a park ranger explained that cannon balls bounced off coquina or, at worst, penetrated a few inches into the walls.

Fort Matanzas National Monument (8635 A1A South) is located 14 miles south of downtown St. Augustine on U.S. Highway A1A; the entrance is 4 miles south of State Highway 206. It's open from 9 a.m. to 5:30 p.m. daily; the ferry (not wheelchair accessible) departs the Visitor Center dock hourly, starting at 9:30 a.m.