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If you need to get from the French mainland to the little island of Noirmoutier, you better hurry, because the road will literally disappear beneath you.

Running almost 3 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. Anyone wishing to travel to and from the island overland has a little over an hour to get there. The journey can’t take too long, because the waters 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 can wait for rescue or the next tidal shift.

Every year the disappearing road is also host to a foot race known as the Foulées du Gois, during which daring runners try to 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 through the road that wasn’t there.

To find out more about the Passage du Gois, check out Atlas Obscura!

More incredible places around the world:

• This historic natural spring in the small village of Tonnerre, France, is nothing short of magical
• Villa Rose is a preserved example of Switzerland’s “false chalets,” World War II forts built to look like suburban homes
• One of the original London bridges is now located in Lake Havasu, Arizona