Puʻu o Mahuka Heiau State Historic Site
Oʻahu's largest heiau, watching over Waimea.
Nearly two acres of stacked stone walls on the ridge above Waimea Bay, likely raised in the 1600s under a ruling chief. The coast view alone justifies the drive up through Pupukea. Open 9 to 5:30, free. Walk around the walls, never on them.