Second Cathedral - Lanai, Hawaii

“You get an idea how the island formed,” says Lahaina Divers’ Erica Heller of this Lanai landmark site with prolific lava structures. Start by swimming through a canyon with walls rising 40 feet, and then descend to 75 feet to a 30-foot-tall lava arch. This site sees a sweeping array of wildlife, including turtles, eagle rays and dolphins, as well as a healthy population of the endemics that have made Hawaii unique: longfin anthias, reticulated butterflyfish and saddle wrasse.