I did a mountain-biking day trip through the Sacred Valley, just outside of Cusco. I stopped to shoot photos at two sites: the agricultural ruins at Moray, and the salt pans (salineras) of Mara which are still in use today. Both were unbelievably impressive.

http://en.wikipedia.org/wiki/Moray_%28Inca_ruin%29 (This wiki article lacks many details but contains links that provide more information on the ruins at Moray.)

http://southamericatravel.suite101.com/article.cfm/salneras_de_maras