Passage du Gois

If you need to get from the French mainland to the little island of Noirmoutier you'd had better hurry because the road will literally disappear beneath your feet. 

Running almost three miles across the Bay of Bourgneuf, the Passage du Gois is built atop a narrow spine of silt that has developed over hundreds of years. Eventually the line grew big enough that it rose out of the waters during low tide, creating a land bridge across the bay. Twice daily, during low tide, the causeway appears and anyone wishing to travel to and from the island over land has a little over an hour to get there. Should the journey take too long the waters can rise back up as though the passage never existed, stranding people and vehicles in the middle of the bay. To prevent such a calamity safety poles have ben placed at intervals down the road so that anyone overstaying their welcome on the road can wait for rescue or the next tidal shift.

Every year the disappearing road is host to a foot race known as the "Foulées du Gois" during which daring runners try and beat the onrushing tides.

Despite the clearly marked signs, a number of people get caught on the road each year, swimming and splashing their way to the nearest safety pole, but not even the clear danger can keep people away from the road that wasn't there.