The waves that created this giant stone amphitheater receded long ago. Now the highway passes right outside the cave, about 3 miles north of Makaha Beach. Kahuna (priests) performed rituals inside the cave's inner chamber, which was the legendary abode of a vicious shark-man, a shape-shifter who lured human victims into the cave before devouring them. Hawaiians consider it a sacred place and won't enter the cave for fear that it's haunted by the spirits of deceased chiefs.
Driving north, it's easy to miss the cave entrance. Look for the wide parking area on the west side of the road.
