Windsock and Mont Saint-Michel. View looking past a windsock towards the rocky tidal island of Mont Saint-Michel (Saint Michael's Mount). The island lies approximately one kilometre off the country's north-western coast, at the mouth of the Couesnon River, near Avranches. It has held strategic fortifications since ancient times, and since the 8th century AD has been the seat of the monastery (shown here) from which it draws its name.