Where: Honolulu, Hawaii
Why it made our list: This former volcanic crater was flooded, and, because it's protected by cliffs on three sides, quickly became filled with 400 species of tropical marine life, like butterflyfish, triggerfish, pufferfish, moray eels, and squid, as well as sea turtles, reef sharks and dolphins. And now, at times, tourist. But Hanauma remains one of the best snorkeling spots in the world – there’s even a concession stand that rents masks, fins and snorkels.
Bonus: You might recognize this beautiful bay from your favorite Scott Caan show, Hawaii Five-0. Guess that’s just a fun fact. The more you know!