Hardly accessible, still visited by thousands a day. Mt. St. Michel

Located in Normandy, one of the most famous European buildings. Being of interest as well for its unusual location on a tidal island.

The internet resources say that around three million people are visiting this place yearly.  As there is only one way in and out, at first sight, you see the crowds. But the island consists of a small village with a couple of narrow streets, fortifications and many chambers or halls on different levels in the monastery itself. In most parts, you can move freely inside. I do not think you can get lost there, but still, it seems a bit like a maze. 

For the most part, the buildings of the Mont St. Michel are thousand-year-old, with many pieces in a Roman style. As the buildings were reconstructed and rebuild a couple of times, some other styles appear, too. From outside you may have the impression the structure is very coherent, but inside you can easily see the additions.