Lanai, Hawaii, United States

First Cathedral (Lanai)

First Cathedral is the larger and more spectacular of the two collapsed lava-tube domes that make up the Cathedrals dive site complex on the south coast of Lanai. Boats from Lahaina, Maui, run the site as part of a Lanai day trip, with the crossing taking about an hour. The chamber inside the dome is large enough for an entire dive class to fit comfortably, with multiple openings, skylights and a sand floor at 14 to 18 metres. Sunlight streams down through holes in the basalt ceiling and reflects off the white sand floor in a stained-glass effect that gives the cathedral metaphor real weight. Penetration is straightforward through wide openings; the site is technically considered overhead environment but in practice is a swim-through. Resident wildlife: white tip reef sharks resting in the side caves, slipper lobsters in the cracks, spotted eagle rays cruising the entrance, large green sea turtles, schools of pyramid butterflyfish on the outside walls. Visibility regularly exceeds 30 metres.