I spent a few weeks in Cusco, Ollyantaytambo and Aguas Calientes, it was incredible. Prior to that I have studied the English explorer Percy Fawcett who spent a lot of time in S. America. In a book written by his son Brian Fawcett, who compiled all sorts of information and diary entries from his father. He has a couple anecdotes about a certain purple flower that had properties which allowed it to "melt" stone and iron. This is the book I am referring to, it's a very interesting read.