Almost 70 miles west of Key West, Florida, lies a cluster of seven small islands known as the Dry Tortugas. These islets of coral reefs and sand, together with the surrounding shoals and waters, are renowned for their birds and marine life and their legends of pirates and sunken gold. Fort Jefferson, the largest of the 19th-century American coastal forts, is a central feature of this area and of Dry Tortugas National Park.

The Tortugas were first discoverd by Ponce de Leon in 1513. Abundant sea turtles, or tortugas, provisioned his ships with fresh meat, but there was no fresh water -- the tortugas were dry.

Since the days of Spanish exploration, the reefs and shoals of the Dry Tortugas have been a serious hazard to navigation and the site of hundreds of shipwrecks.

U.S. military attention was drawn to the keys in the early 1800's due to their strategic location in the Florida Straits. Construction of a massive fortress began in 1846, but the fort was never completed -- the invention of the rifled cannon made it obsolete.

• Explore coral wonderlands and bright tropical fish in just three or four feet of warm, subtropical water.