A stunning natural spot of huge and fascinating rock formations set amid rolling green hills at an elevation of 3,400m (11,150 ft.), Cumbe Mayo has been called a stone forest. Equally remarkable, if not more so, is the evidence of human intervention here, first discovered in 1937: caves etched with petroglyphs and a pre-Inca aqueduct that is a marvel of hydraulic engineering. The remarkable open canal, carved out of volcanic stone in perfect, polished lines, served to collect and redirect water from various sources on its way to the Pacific Ocean. At points, the canal narrows and introduces right angles to slow the flow of water and lessen the effects of erosion. In all, the aqueduct stretches more than 9km (5 1/2 miles). Created, incredibly, around 1000 B.C., it is perhaps the oldest known man-made structure in South America.
Elsewhere in the park is a cliff referred to as the sanctuary, which looks like a human head from the outside; a grotto inside is adorned with enigmatic petroglyphs and is said to have been a place of ritual. Stairs carved in stone lead to sacrificial altars (llamas, not humans) and platforms, signs of the ceremonial importance of the zone. As guides lead groups through the "stone forest," they point out figures that can be seen in the stones, such as a group of monks as well as phalluses, breasts, a dog climbing a hill, a tortoise, a pirate's head, and mushrooms. Some are clear, amusing likenesses; others are like trying to identify someone else's images in cloud formations.