Parque Nacional Isla del Coco

Around 500km southwest of the Costa Rica mainland, Isla del Coco is a natural wonder that teems with wildlife, including the largest schools of hammerhead sharks on the planet. For that reason, divers descend from all corners, often venturing out on liveaboard trips with companies like Aggressor and Undersea Hunter. There's also some fascinating pirate history here, and apparently some buried treasure.