If you happen to be caught in heavy rain at Machu Picchu, take the opportunity to see the ancient Incan storm drainage system in action. An elaborate system of channels funnels rainwater off the side of the mountain and rivals modern municipal drains. This is surely a major factor in Machu Picchu's survival to the modern era.
This dusty highway along the Peruvian coast is actually part of the Pan-American Highway. An adventurous soul could theoretically follow the highway from South American to Alaska, though in practice the highway is not contiguous and you would have to arrange cargo boat service to cross the Darien Gap between Colombia and Panama.