Mont Saint-Michel (St Michael's Mount) is a tidal island in Normandy, France. The Wikipedia entry details its fascinating history, including this:
Before the construction of the first monastic establishment in the 8th century, the island was called Mont Tombe. According to legend, the archangel Michael appeared to St. Aubert, bishop of Avranches, in 708 and instructed him to build a church on the rocky islet. Aubert repeatedly ignored the angel's instruction, until Michael burned a hole in the bishop's skull with his finger.
Here's photos of the surrounding area and causeway:
Here's shots of the abbey:
Here's the abbey from above:
Here's a few interior shots:
Finally, here's the abbey's official site.
*Previously: O'Brien's Castle in Ireland.