The Sacred Cenote — a natural limestone sinkhole 60 meters across, used for ritual offerings for over a millennium. Dredging in 1904 and 1967 recovered gold discs, jade ornaments, copal incense, pottery, and the bones of men, women, and children. It was still being used as a pilgrimage site when the Spanish arrived.
Gary Todd from Xinzheng, China, CC0, via Wikimedia Commons