Known as Waiahuakua, this is the second longest sea cave in the world, stretching 1,155ft. It is known as the Sacred Water Cave and as the Double Door cave – as it has both an entrance and an exit. Kayak tours run through the cave to allow visitors a close-up view of the caverns huge length. A fissure in the roof of the volcanic rock allows water to gush into the amazing cavern.
Open Ceiling Cave on Na Pali Coast, Kauai, Hawaii, USA. This cave is a hollowed-out lava tube, and may have served as a place where ancient Hawaiians could rest in their canoes when traveling along the coast. Photo by threeifbysea (Instagram)