If you snorkel only once while you're here, make it at Olowalu, home to Maui's most diverse marine populations. Slap on reef-friendly sunscreen and join all sorts of wonders along 40 hectares (99 acres) of some of Hawaii's healthiest coral structures. Watch manta rays and green sea turtles rock up to cleaning stations, or peer inside a nursery for blacktip reef sharks, among the 500-year-old coral head formations. Less of a swimmer? Then try a stable wide-bottomed ocean kayak for a different perspective.