We are in the Inca Sacred Valley, and there are Inca ruins all over the place. After visiting the main ones near Cusco yesterday, we took a local business to Pisaq, hired a taxi, and went up the hills to follow the trail there. The trail hugs the edge of the hill, and the views of the valley and surrounding hills, and the old Inca towns, are fantastic.
The way they brought huge stones from a quarry many kilometers away, up a hill on trails barely wide enough to walk, and then fitted them together without cracks or mortar, is amazing. Too much free manpower I suppose. The walls still stand today as they were built, although the roofs were lost.