Dry Tortugas National Park United States

Legendary

Accessible only by seaplane or boat, this isolated park preserves Fort Jefferson and the Dry Tortugas islands.

Photo by NPS Natural Resources

Look closely at Fort Jefferson's walls and you'll spot a line where the color changes. Below it the bricks are one shade. Above it they're another.

That line marks the start of the American Civil War. The fort's brick supply came from the South, and when war broke out in 1861, builders had to switch to bricks shipped down from New England instead.

The fort sits on a tiny island 68 miles west of Key West, Florida. Getting there takes a boat or a seaplane, since no road comes close.

Spanish explorer Juan Ponce de León found these islands in 1513. He caught more than 100 sea turtles here, so he called them Las Tortugas, meaning "the turtles."

Sailors later added the word "Dry" to their maps. It was a warning that the islands had no fresh drinking water at all.

The United States began building Fort Jefferson in 1846 to guard shipping routes through the Gulf. Workers hauled every single brick in by ship, more than 16 million of them.

Enslaved people, hired workers, and military prisoners did the building. The walls ended up 8 feet thick and 50 feet tall.

It's the largest brick building in the Americas. It's also unfinished.

Construction dragged on for about 30 years and simply stopped. New cannons invented during the Civil War could smash straight through brick, which made the whole design outdated before it was done.

No enemy ever attacked it. Instead, the fort became a prison.

Its most famous prisoner was Dr. Samuel Mudd, a doctor who treated John Wilkes Booth's broken leg after Booth assassinated President Lincoln. Mudd was sent here for life, but he was pardoned in 1869 after helping fight a deadly yellow fever outbreak among the soldiers.

Snorkel right off the beach, where coral grows on the old fort walls under clear, shallow water. Walk the top of the fort for views across open ocean in every direction. Watch for sea turtles and nesting seabirds, since almost the entire park is water and wildlife.