More than 100 years ago an American explorer found Machu Picchu, the Lost City of the Incas.
It was build in the 15th century by the incas and abandoned a century later due to Spanish Conquers. It is a breathtaking live monument that everyone should visit. I recommend doing the Lares trek, which is less popular but with more scenery landscapes and with many local villages interactions.
Tour guide: http://www.cusitravel.com