Snorkeling the Glistening Waters of Hanauma Bay. This underwater park, once a volcanic crater, is teeming with a rainbow of tropical fish. Bordered by a 2,000-foot gold-sand beach, the bay's shallow water (10 ft. in places) is perfect for neophyte snorkelers. Arrive early to beat the crowds -- and don't forget that the bay is closed on Tuesday. Aloha Dive Shop, Koko Marina Shopping Center (tel. 808/395-5922), can set you up with fins, mask, and snorkel for just $7 a day.