Plumb the depths of the Caribbean via submarine in Roatan.   (Photo: Annick McIntosh/Courtesy of Stanley Submarines)

Its proximity to the world’s second-largest barrier reef makes the 50-square-mile Honduran island of Roatan a magnet for a special breed of marine-life geek. Self-taught submarine builder Karl Stanley takes travelers on reef dives off Half Moon Bay in his homemade three-passenger craft, Idabel. Unless you’re James Cameron, there’s no other way to go this deep: Stanley Submarines ­expeditions (from $400; stanleysubmarines.com) range from 90 minutes to nine hours and descend to 2,000 feet—or about 1,940 feet farther than the average scuba trip. On the way down, you’ll glimpse bio­luminescent coral and feather-duster­like sea lilies, as well as deep-dwelling Dumbo octopuses and elusive six-gill sharks that have never seen the light of day ­(or ­humans). Back on shore, bypass the West Side’s touristy beach-­bar scene—particularly when the cruise ships dock—in favor of the ­minimally developed East End. Primo lodging can be found at the upscale Las Verandas Hotel and ­Villas (from $245; las-verandas.com), which welcomed its first guests last month. Also worth a stop: the newly opened 160-acre Blue Harbor Tropical Arboretum (tours $13; Main Rd.; blueharbortropicalarboretum.com), where guides dole out samples of ripe ­guavas, sweet limes, and creamy soursop straight from the trees. At remote Camp Bay, professional kite surfer Marilou Lavallée hosts private lessons just off the two-mile-long white-sand strand ($75 per hour; e-mail kitesurfroatan@gmail.com to book). Refuel after a day of riding at the tiny La Sirena de Camp Bay (504-9564-6866), a thatched-roof hut plunked on the end of a wooden pier, where intrepid epicures are rewarded with stiff rum punch, spicy lionfish ceviche, and just-caught lobster.

The thrill-o-meter: A rip-roaring, heart-on-the-floor rush—better buy travel insurance.