This is Mont St. Michel in Normandy, France. It is a one of a kind example of architecture that features both Romanesque and Gothic architecture, most of it is Romanesque. The Abby at the top of the island is mostly Gothic inside. Would love to visit and experience it's wonderful architecture.
Castle house island - Dublin, Ireland | Incredible Pictures
Castle Liechtenstein, Lower Austria, by arjuna_zbycho, via Flickr