Dry Tortugas National Park

Nearly 70 miles west of Key West, this remote island park centers on Fort Jefferson, a massive unfinished 19th-century coastal fortress of 16 million bricks that once held the Lincoln assassination conspirator Dr. Samuel Mudd. Seven tiny islands shelter coral reefs, sea turtles, and great sooty tern colonies.

Snorkel the shallow reefs right off the beach, explore the fort's casemates, and camp under the stars. For a challenge, snorkel the offshore wrecks and coral heads or kayak the open water between the keys.