Mount Penha, Guimaraes- history of boulders?
 

I was recently in Portugal and one of the cities that impressed me the most was Guimaraes. One of places not listed in my guide was Mount Penha (reachable from the city via a cable car). Very nice place. The Penha Sanctuary that is on the top is surrounded by HUGE boulders. I could not find any information regarding how these boulders got where they are, etc. Does anyone on this forum know?