Dry Tortugas — Fort Jefferson, 70 miles west, and the reef nobody talks about

Dry Tortugas National Park is 70 miles west of Key West, in the middle of open Gulf water, and it is one of the least-visited national parks in the continental United States. About 80,000 people a year make it out. Yellowstone gets that in three days. That's not because the park isn't worth it — it's because getting there is a commitment.

The park is 100 square miles of open water and seven small islands. The centerpiece is Fort Jefferson on Garden Key — a hexagonal masonry fort with 16 million bricks, built by the U.S. Army between 1846 and 1875 as the largest coastal fortification in the Western Hemisphere. It was designed to guard the Gulf shipping lanes. It was never finished. The Army abandoned it in 1874 after 30 years of construction because the foundation was sinking into the coral and rifled artillery had made masonry forts obsolete. It's essentially a $250-million (in 2026 dollars) 19th-century engineering failure that became a national park.

Getting there: two options. The Yankee Freedom III ferry runs daily out of the historic seaport, leaves at 8 a.m., arrives around 10:30, gives you about 4 hours on the island, back in Key West by 5:30 p.m. It's about $220 per adult, includes lunch and snorkel gear. The other option is a private day-trip charter — 35' to 37' center-console boats out of Key West that run 8 to 12 hours door-to-door with smaller groups. Costs more, gets you to the moat wall and offshore reefs the ferry doesn't reach.

The reason to go — beyond the fort — is the snorkeling. The moat wall around Fort Jefferson is a coral wall in 6-15 feet of water, running the entire hexagonal perimeter. Elkhorn coral, staghorn coral, tarpon, nurse sharks, spotted eagle rays, sometimes a goliath grouper. It's inside the boundary of a no-take zone that's been protected since 1935. The water clarity is regularly 80-100 feet. The soft-coral and gorgonian density is what Florida Keys reefs looked like before the 1980s coral disease. If you've only ever snorkeled at Looe Key or the Sand Key light off Key West, the Tortugas is a different order of magnitude.

Beyond the fort: Bush Key (bird sanctuary, closed most of the year for sooty tern nesting — 100,000 birds), Loggerhead Key (the lighthouse and the historical wreck of the Windjammer), and open-water dive sites like the Windjammer Wreck and the Bird Key Bank if you're on a charter.

The fort itself takes about 90 minutes to walk. Free ranger-led tours run twice a day. The stories are what stick: Dr. Samuel Mudd — the physician convicted of aiding John Wilkes Booth's escape after the Lincoln assassination — was imprisoned here from 1865 to 1869. His cell is preserved. The yellow fever epidemic of 1867 killed nearly 40 of the fort's soldiers; Mudd, previously convicted, worked as the fort doctor during the outbreak and was pardoned by Andrew Johnson in 1869 partly for that service. The fort was decommissioned as a prison in 1874 and gradually forgotten. Franklin Roosevelt made it a National Monument in 1935 (Category 5 hurricane year — the same season) and it became a National Park in 1992.

What to bring: mineral sunscreen (the reef around the fort is protected, and zinc oxide or titanium dioxide is gentler on it), water shoes for the coral rubble on the beach, cash for the ranger station donation box (there's no ATM, no cell service, no store — the park is genuinely off-grid), and a hat. There is no shade on the parade ground.

Worth it question: yes, if you have a full day, if you don't get seasick easily (the crossing is 2+ hours in open water), and if snorkeling matters to you. If you only have one day in the Keys and you've never seen the reef, this is the trip that will change your idea of what Florida looks like underwater.