Seventy miles west of Key West, Dry Tortugas National Park emerges from the Gulf of Mexico like a mirage. This remote park is mostly open water with seven tiny islands, home to massive Fort Jefferson, vibrant coral reefs, and rookeries of sooty terns and frigatebirds. Accessible only by boat or seaplane, it invites adventurers to snorkel shipwrecks, camp under starry skies, and experience frontier solitude.

In the heart of the sea, where the azure waters weave tales of ancient mysteries, lies an oasis of tranquility—the Dry Tortugas National...