Costa Rica's Pacific coast is famous, but it is the **isolated Cocos Island** — 550 kilometers offshore — that has earned the country its place among the world's elite dive destinations. Designated a UNESCO World Heritage Site and protected as a national park since 1978, Cocos is reachable only by liveaboard after a 32–36 hour crossing, and what awaits beneath the surface justifies every nautical mile. **Bajo Alcyone**, the most famous seamount in the eastern Pacific, rises from 300 meters of open ocean to a plateau at 25 meters. Schooling **scalloped hammerhead sharks** form silver walls of hundreds — sometimes thousands — of individuals, particularly between June and November when warm and cold currents collide. Galapagos sharks, silky sharks, and the occasional whale shark complete the pelagic theatre. **Manuelita Island**, just minutes from the anchorage at Chatham Bay, offers night dives that are legendary among shark divers. Whitetip reef sharks abandon their usual passive behavior and hunt in coordinated packs across the reef, swarming over coral heads in pursuit of sleeping fish. Few dives in the world deliver such raw predator action. **Dirty Rock** and **Big Dos Amigos** are the other signature sites — pinnacles and arches that channel current and concentrate marbled rays, eagle rays, tiger sharks, and the elusive **smalltooth sand tiger shark**, a rare species whose recent identification at Cocos was a milestone for shark research. Bottlenose dolphins frequently join divers, and silky sharks circle the boat between dives. On the mainland, the **Bat Islands** (Islas Murciélago) off Guanacaste are accessible from coastal resorts and famous for reliable encounters with adult **bull sharks** between May and November. The Catalina Islands offer manta rays and seasonal whale shark sightings, while the **Caño Island Biological Reserve** in the south provides easier diving with white-tip sharks, turtles, and large schools of snappers. Costa Rica also offers some of the most diverse topside experiences in the Americas — cloud forests, active volcanoes, and rainforests teeming with monkeys, toucans, and sloths. Combined with year-round water temperatures of 24–28°C and strong marine protection laws, Costa Rica is a destination for advanced divers chasing big animals in big blue water.