Costa Rica
Best overall months to dive: Jun–Nov
Costa Rica has coastal diving on both the Pacific (Guanacaste, the Catalinas, Bat Islands) and Caribbean sides, but its marquee dive destination is Cocos Island, about 550km (342 miles) off the Pacific coast. Cocos is reachable only by liveaboard, on a roughly 36-hour open-ocean crossing each way from the port of Puntarenas. It draws divers for its dense scalloped hammerhead schools and other pelagics, not for reef or macro diving. Mainland Pacific sites are far more accessible and cheaper but are a different, lower-key experience.