A sunken volcanic crater forming a crescent island, the sheltered inside is 30m-viz snorkelling over reef, and the back wall…A sunken volcanic crater forming a crescent island, the sheltered inside is 30m-viz snorkelling over reef, and the back wall drops off into open ocean with whitetip reef sharks, manta and Hawaiian endemics (25% of Hawaii's reef fish exist nowhere else). Humpback song fills the water in winter. A 230,000-year-old volcanic cinder cone. Used as a US Navy bombing target in WWII (unexploded ordnance was cleared for decades), then protected as a conservation district in 1977. Now Maui's most-visited marine site, go at dawn. Anchorage: Day moorings inside the crater; a State Marine Life Conservation District, no anchoring on coral. Hazards: No site-specific hazards noted, brief normally. Plus