The surrounding ocean is the reason Cocos Island ended up on the world-heritage list. Schooling hammerhead sharks - sometimes dozens, sometimes hundreds at a time - aggregate around the island's submerged pinnacles and have made it one of the most famous dive destinations on the planet. White-tip reef sharks rest on the sandy bottoms in piles. Marbled rays glide past. Whale sharks pass through on the seasonal currents. Dolphins, giant moray eels, and sailfish move in and out of the bigger picture. To protect all of it, Costa Rica has progressively expanded protections around the island, turning it into a solitary green dot at the center of a vast marine reserve now covering tens of thousands of square kilometers.

The island's pirate lore is thick enough to have inspired its own literature. Three of history's supposedly largest treasure caches are said to lie buried here - among them the hoard of Lima, which a British captain named William Thompson allegedly stashed on Cocos in 1820 while fleeing the advance of José de San Martín's army. Over the last fifty years, more than four hundred formal expeditions have combed the bays, ridges, and caves. Thousands of smaller searches have added nothing. Costa Rica now prohibits treasure hunting outright. The forest keeps what it keeps.

Cocos is rugged, dense, and relentlessly wet. Its twenty-four square kilometers of land contain more than two hundred waterfalls, three sheltered bays, and tropical forest that averages rainfall measured in meters rather than millimeters. The tops of the interior cliffs disappear into cloud most afternoons. No animals reached the island on their own - the pigs, dogs, and cats you might encounter were all brought by humans, and some of them are still a management problem for the rangers. The climate is hot, humid, and almost perpetually on the edge of a rain shower, with brief dry breaks between March and December.

Access is deliberately hard. Cocos is a thirty-six-hour boat ride from the Costa Rican port of Puntarenas and requires a government permit. Overnight stays on shore are prohibited for tourists - you sleep on your live-aboard dive boat, not on the island. The main trips are run by the Okeanos Aggressor and the Undersea Hunter, both of which base their operations around the schooling sharks and the dramatic pinnacle dives. If you want to set foot on the island, you do it by ranger permission, at one of the few safe landing points, and generally as part of a guided hike to the high ground for the view that almost no one gets to see.

For most visitors, the day revolves around the water. Two or three dives in the morning and afternoon, with the surface time spent watching frigatebirds wheel against the cliffs. Snorkeling in the bays is a less extreme alternative. A hike to the summit is worth the grind if the rangers have a slot - the view takes in both flanks of the island, the anchorage below, and a sea that often has nothing else in it. Sharks and eels are the obvious hazards, but the bigger risk is the one that defines the whole place: you are a long, long way from anywhere, in a park that belongs first to the ocean and only barely to people.