Tidal roads or causeways exist all over the world but Passage du Gois in France is the longest among them - it goes for about 4.15 km and according to wiki in early days it was even longer when the old dikes were farther from the coast.
It is located in France in the department of Vendée and connects island Noirmoutier with the mainland. Before Baie de Bourgneuf silted up during the XVI century it was accessible only by boat. Later when the moving of silt stopped the road was paved with cobblestone and transportation services were offered by carts. It seems that origin of the word Gois is still debatable as I found at least two versions - the name Gois may have derived from old French and is the same origin as the modern word gué (forded) or it comes from the verb "goiser" which means to walk while wetting one’s shoes. I like the latter a little more but I guess both can be true. In 1701 the passage was first mentioned on a map.
Only twice a day when tide goes out the road becomes accessible to visitors and the rest of the day it lies under 1.3 to 4 meters of water so inevitably it became an attraction to many people - some come to see the road, drive, cycle or run, others come to gather shells. And it is not used just as a road, since 1986 a foot race takes place along the passage "Foulées du Gois" every year and even Tour de France used it as a track in 1999 for the first time. It did not go very well as after water leaves, the stone paved road is covered with weeds and is rather slippery and, of course, a fall was inevitable that ruined hopes for a victory for some of the favorites of the race. Still in 2011 the first stage started from here and it was recently announced that in 2018 the race will use the passage during the first stage again. I sincerely hope this time participants will be more lucky.
Tour de France 2011 crosses the Passage du Gois (TV video still) http://road.cc/content/news
At this point you may wonder if there are any regulations on how to use the road not to get in trouble. Signs with precise times of tides are available on each side of the passage but still people get caught midway every year as the rate at which road is flooded is very high and people just do not expect that. Overall the road is accessible for several hours at a time. Rescue towers were erected along the passage so that people can get on them and wait for rescue or until the tide goes out while taking photos of their cars drowning. I was rather curious about statistics on accidents and it turns out that these towers had saved a lot of lives, fortunately, the towers are more often used as a backdrop for photographing than as a shelter.