Exhausted by the languor of lying on a beach? In search of Caribbean adrenaline, Rupert Isaacson finds a treasure chest of activities for the intrepid traveler

The first reef shark appears just as we've finished forming a huddle on the sandy ocean floor, somewhere off the sunlit island of Grand Bahama. The shark is impressive, all eight elegant, deadly-looking feet of him—or perhaps, her, for the females are larger than the males. Despite our dive master's instructions—"Clump yourselves together. That way they'll think you're coral. Just don't reach out, whatever you do"—the urge to flee is instinctive. Assuming you could make it up to the boat unbitten, the speed of the ascent would give you the bends. Nothing for it but to stay put, breathing deep, bubbles floating upward like prayers.

Six or seven sharks are circling us now, getting closer as Ricky appears, having descended like some conquistador of old in a full suit of chain mail. Holding tight to his container of frozen fish bits, he stomps toward us and comes to a slow-motion halt perhaps five feet away. He opens the tube. With frightening speed, the sharks zero in, passing so close that we get bumped by tails, bodies, fins.

Amid the frenzy are other meat-eating fish: Athletic skipjack tunas flit between the sharks, relying on speed to keep them safe; heavyset groupers with jutting underbites full of wicked-looking teeth lurk at the edges, grabbing what they can. One grouper decides that the V between my legs is the perfect refuge from the fray. Watching him dart in and out and seeing those sharp teeth just below my swim trunks causes my entire reproductive apparatus to shrink back into my body. Or so it seems.

Ricky reaches out suddenly, grabs one of the sharks, and rubs his metal glove over the sensors on its snout, sending the creature into an instantaneous trance. Its terrifyingly neutral eyes half-close. Ricky shunts the long body toward me, nodding for me to risk a touch. I do. The skin is wonderfully smooth. I have just enough time to think, My God, I'm touching a shark, before the creature comes to, lunges, and rasps its teeth across Ricky's chain mail arm.

The Bahamas—in fact the caribbean in general—might seem an unlikely place to come in search of adventure. Most people quite rightly associate these islands with sybaritic resort vacationing. But with a rising tide of travelers looking for more from the islands than a suntan, even big resorts are allowing guests to experience the mountains, rain forests, reefs, and caves outside the perimeter fence.

In devising my own mix of adrenaline-fueled adventures, I soon realize that there is already almost too much choice. Seasonal limitations help narrow the options: For example, diving with humpback whales off the Silver Banks, north of the Dominican Republic, can be done only in the spring, and I want to travel in October. I choose three islands: Grand Bahama is one of the few Caribbean islands to offer shark diving as well as swimming with dolphins; the Dominican Republic, whose ten-thousand-foot Pico Duarte is the highest mountain between the Rockies and the Alps, is known for its horses and rugged terrain; and in Trinidad, in the far southeast, one of only two islands with a Carib Indian population, there is a shaman who will lead me into the rain forest.