"Moray (3,500 meters) lies 74 km from the city of Cusco. It is famous for its sunken amphitheater, made up of four circular terraces which appear to disappear into the earth like an artificial crater. The site was apparently an Inca agricultural research station designed for experimenting with crops at various altitudes (some of which run down to depths of 100 meters). It is believed that the terraces, built over containing walls filled with fertile earth and watered by complex irrigation systems, enabled the Incas to grow more than 250 plant species."
(click to enlarge)
(click to enlarge) Note the steps: Slabs of rock projecting from the faces of the terraces.