A great introduction to the ocean floor for nondivers, the world's largest passenger submarine descends within view of Diamond Head and Waikiki's skyline. It churns down to 100 feet, sometimes passing eels, green sea turtles, and even majestic whale sharks. It tours by several artificial reefs, including a sunken Navy oiler and a Korean fishing boat. Massive viewing ports—one per person—make it easy to soak it all in. The 1.5-hour excursion departs from the Hilton Hawaiian Village at Port Hilton and remains a popular way to share the sea's beauty safely and comfortably for kids and less mobile travelers (the roomy sub seats 64 and even has air-conditioning!).