Which UNESCO World Heritage Site in France is a medieval island commune topped by an abbey?

Mont-Saint-Michel and its Bay is the UNESCO World Heritage Site centered on a medieval island commune topped by an abbey.

Mont-Saint-Michel is a tidal island off Normandy, France. Its buildings rise around a rocky summit crowned by the Benedictine abbey of Mont-Saint-Michel. The settlement developed as a religious destination and later became a fortified medieval town, with narrow streets and buildings climbing the steep island.

The site is especially notable for the relationship between architecture and the surrounding bay. Tides can dramatically change the appearance of the landscape, although modern works have altered water and sediment movement over time. The abbey's construction unfolded over many centuries, creating a complex mixture of Romanesque and Gothic elements.

UNESCO inscribed Mont-Saint-Michel and its Bay in 1979. A frequent mistake is to call the entire site a castle: the island was fortified, but its defining summit monument is a Christian abbey. The causeway and later access arrangements also mean that the modern visitor experience differs from the medieval island's isolation.