Le Passage du Gois in Metropolitan France

You're standing at the Passage du Gois, a road that runs for more than four kilometres straight through the sea. On one side is Beauvoir-sur-Mer on the mainland of the Vendée, on the other the island of Noirmoutier. Twice a day this road disappears completely under the tide. At low water you can drive or walk across. At high water, all you see is sea.