Is it a castle or an island? Is that the desert or the sea? Is it Bretagne or Normandie? Each day, this castle becomes an island, then the sea withdraws to leave treacherous sands behind. Meanwhile, a whimsical little river draws the border between the two realms, making Mont St. Michel part of Normandy. The mountain has always been a place of awe; beautiful and inaccessible, it caused many to perish at the mercy of tides. And as it happens with so many places of awe and beauty, it has always been a site of worship. In the early days of Christianity, monks were using Mount Tomb – that was…