Mont Saint Michel!
At low tide a narrow land bridge connects the island to the main land. However, at high tide, the bridge is quickly covered over by 14 meters of water. Even at low tide the land bridge is dangerous, with quicksand traps on it that cannot be charted because they shift with each new tide.
There are no regular ferries to or from the island. People must generally wait for the tide to go out before traveling to or from the island.
In the 8th century the Archangel Michael appeared to Bishop Aubert of Avranges, and demanded that a church be built in his honor. Since then, various building projects have occurred, adding on to the church and abbey. The most extensive construction occurred in 1020, under Abbot Hildebert, who laid a masonry foundation across the entire island. Most of the buildings present now were completed by 1135, but several new buildings were constructed after a fire in 1203 (including The Marvel -- a grand building collecting dining halls, cloisters, kitchens, and dormitories). The weakness of the foundation led to the collapse of one of the towers and one of the original churches in the 14th and early 15th centuries, but reconstruction of the damaged buildings didn't occur until the 16th century, because of the Anglo-French war in progress. In 1632 most of the buildings are in good condition, except for the pair of towers facing out on the west side of the church (built by Abbot Robert de Torigny in 1170) which is beginning to slouch noticeably.
Mont Saint Michel's reliquary contains artifacts of several French saints, including a cobblestone stained with Saint Blodgett's blood, a bowl used by Saint Katherine, and a tooth of Saint Cameron.
This game is a Subterranean Homesick Games production.