Diving the Deep at Cocos Island

Rated one of the top diving destinations in the world, Isla del Coco is uninhabited and remote (32 hours by boat), and its waters are teeming with marine life. It's no place for beginners, but serious divers enjoy 100-foot visibility and the underwater equivalent of a big-game park. Scalloped hammerheads, white-tipped reef sharks, Galápagos sharks, bottlenose dolphins, billfish, and manta rays mix with huge schools of brilliantly colored fish.

Encompassing about 22½ square km (9 square miles), Isla del Coco is one of the largest uninhabited islands on Earth. Its isolation has led to the evolution of dozens of endemic plant and animal species. The rocky topography is draped in rain forest and cloud forest and includes more than 200 waterfalls. Because of Isla del Coco's distance from shore (484 km [300 miles]) and its craggy topography, few visitors to Costa Rica—and even fewer Costa Ricans—have set foot on the island.

Costa Rica annexed Coco in 1869, and it became a national park in 1978. Today only extremely high-priced specialty cruise ships, park rangers, volunteers, and scientists visit this place. The dry season (December to April) brings calmer seas and is the best time to see silky sharks. During the rainy season large schools of hammerheads can be seen, but the ocean is rougher.

Two boats, Okeanos Aggressor and Undersea Hunter, offer regular 8- to 10-day dive cruises from Puntarenas that include three days of travel time on the open ocean and cost roughly $5,000 to $6,000, depending on the boat and dates.