In the hills just a couple minutes from the center of Cusco is an example of some of the finest Incan stonework -- Sacsayhuaman.  Often the butt of jokes due to the similarity of its name to the English "Sexy Woman", it was probably a religious temple.  The zig-zag formation of three tiers is almost all that remains today, so the exact purpose of the site is not known.  Some believe is was a kind of military garrison.