The stone from this quarry has been used for hundreds of years to build the Opéra, Paris City Hall, the Conservatoire National des Arts et Métiers, the cathedrals of Auxerre and Sens and many other public buildings. The extraction of blocks of stone has left impressive caves bearing the marks of spears and needles, the only tools used by quarrymen for centuries. You can visit the site via a fun digital trail, using the Legendr app to solve this riddle.