One of the best things I did so far in Peru was the hike to Choquequirao, near Abancay. It is a fairly easy, four day hike although many do it in five days and most tourists hire mules and guides. It is doable in three days but it's over thirty kilometers each way with a thousand meter-deep valley in the middle, so it's nice to have a little time. In total, over four days I saw less than twenty tourists, and the place is huge.
I did the hike with a Spanish tourist, and on the way back we linked up with a French tourist who had a mule and a guide, and was returning from an unsuccessful attempt to trek all the way to Machu Picchu (the rivers are swollen, due to the rainy season). Here they are, walking back:
Here are some of the ruins at Choquequirao, with an Andean condor in the lower left corner:
This is the famous "Sector Llamas," with designs worked into the terracing work. This is the most active excavation area right now. Of the 70% of the ruins that are still buried in vegetation, the lower "Sector Llamas," with similar designs except with loads on the animals, is next for excavation.
This is the "Casa de la Caída del Agua," near the bottom of hundreds of incredible terraces on the other side of the mountain from Sector Llamas:
Here is the Plaza Principal, with its temples and two-story houses. The terraces in the lower right have two meter-high walls: