Hawaii’s infamous Halona Blowhole sits in Hanauma Bay, off the island of Oahu. Most visitors are camera-snapping tourists eager to capture 30-foot high mist ejections and frequent whale sightings, but the volcanic rock formation has a more sinister side. Divers and snorkelers have found that the site, nicknamed the "Pinball Machine," is particularly dangerous due to strong currents, hazardous coastlines, and lack of lifeguards. In fact, Halona Blowhole has seen more fatalities than any other dive site in Hawaii.
YOU NEED A diving certification. Your guide will probably want to check your abilities by doing a couple of extreme dives with you before taking you to the Blowhole.
HOW TO DO IT Pick the right conditions: wait for a slack (incoming) tide and stay within 100 feet of the shore. Also, keep your eyes peeled for marine life. It’s one of Hawaii’s most diverse dive sites, where you can spot green sea turtles, butterflyfish, and Spanish dancers. And, if you're lucky, you'll even be able to hear nearby whales and dolphins. ($700; oahuscubadiving.com)