Straddling Brittany's border with Normandy is the spectacular Abbey of Mont-Saint-Michel, which rises like a dream from the coastal flats of the Atlantic. It must be seen to be believed. Located about 175 mi/282 km west of Paris (close to Normandy), the Abbey was built in the 10th century. The cathedral-citadel sits atop a 260-ft granite promontory. At high tide, the place becomes an island; at low tide, a sandy causeway links it to the mainland (be aware that the tide comes in very quickly).