You may also want to check the local regulations about using guides. Many parts of Peru require that you take a guide--partly to provide employment for the locals, and partly to make sure that you don't steal or destroy archeological items.

Our experience with guides there was pretty good...but we did learn of a group that was turned around and escorted out of the mountains because they had no permits or guides.
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Check our our website: http://www.backpackthesierra.com/

Or just read a good mystery novel set in the Sierra; https://www.amazon.com/Danger-Falling-Rocks-Paul-Wagner/dp/0984884963