The sacred grotto at Massabieille, near the town of Lourdes in southern France, appeals to Catholics like no other place. This is the shrine of Our Lady of Lourdes, the place where Mary appeared to a humble peasant girl named Bernadette Soubirous in 1858 and spoke words of comfort and simple faith. At Mary's behest, Bernadette dug in the rocky soil of the grotto and struck water. A puddle soon became a spring that gushed forth waters that were...