The Moray archaeological site consists of a small collection of circular terraces sitting in small depressions on a high plateau above the Urubamba valley, around 3500m above sea level. There is a sophisticated irrigation and drainage system that still works: local farmers planted crops in the terraces as late as the 1970s, before the site was handed over to the National Institute of Culture for preservation.
The terrace walls absorb heat from the sun during the day, and shield the lowest levels from wind, meaning that there can be a temperature difference of as much as 15 Celsius between the top and the bottom. Most archaeologists believe that these terraces were used as an experimental farm by the Incas, to simulate growing conditions at a range of altitudes and determine where different crops would grow best. I also found references to (unnamed) studies that are claimed to show that soil was imported from different parts of the Inca empire, which would support this theory.
Other theories suggest that Moray was a religious site, or, less plausibly, a landing pad for UFOs. The best source I found on line was an article by Roger Atwood in vol. 60 #5 of Archaeology. If you'd like to do more research, then please do let me know what you find out.
We visited Moray on a day trip from Ollantaytambo. Our hotel organised a driver for S/140, which also got us to Chinchero and the Maras salt mines. Entry is by boleto turistico.