Much of the most impressive stuff are invisible in MachuPicchu

While the Inca are best remembered for their beautiful walls, their civil engineering projects were incredibly advanced as well. (Especially, as is often noted, for a culture that used no draft animals, iron tools, or wheels.) The site we see today had to be sculpted out of a notch between two small peaks by moving stone and earth to create a relatively flat space. The engineer Kenneth Wright has estimated that 60 percent of the construction done at Machu Picchu was underground. Much of that consists of deep building foundations and crushed rock used as drainage. (As anyone who’s visited in the wet season can tell you, Machu Picchu receives a lot of rain.)