Raja Ampat, Indonesia

Raja Ampat boasts the highest marine biodiversity on Earth, with over 1,500 fish species and 600 coral species. A single dive reveals more variety than the entire Caribbean combined, outperforming #5's species count by a factor of three. Waters average 28°C year-round, and divers encounter everything from epaulette sharks to walking gobies, protected by conservation laws covering 90% of the archipelago.