Riders in the 2018 Tour de France will set off from the Passage du Gois, a causeway that the Atlantic Ocean tides cover twice a day.
With this year's race set to start in the German city of Dusseldorf, cycling's biggest event will return home for its Grand Depart in 2018.
Tour organisers unveiled the first three stages of the 2018 route, which will start in the western Pays de La Loire region on June 30.
Stage one will take the peloton on a 195-kilometre ride from Noirmoutier-en-l'Ile to Fontenay-le-Comte.
Sprinters will have a chance to grab the yellow jersey the next day between Mouilleron-Saint-Germain and La Roche-sur-Yon, a town that will host its first stage finish since 1938.
Stage three will be a 35-kilometre team time trial in Cholet, and Stage four will start from the posh sea resort of La Baule, with the peloton heading north. The remainder of the route is to be announced in October at the official race presentation.
The Passage du Gois featured in the 2011 race.
The Gois is a four-kilometre road flooded by tide twice a day, linking the island of Noirmoutier to the mainland, and has contributed to race lore.
In 1999, a handful of Tour favourites had their victory hopes ended in a massive crash on the Gois, which was still partially covered by the sea.
Opening stages of the 2018 Tour de France:
Saturday, 30 June – Stage 1: Noirmoutier-en-l'Île to Fontenay-le-Comte, 195km
Sunday, 1 July – Stage 2: Mouilleron-Saint Germain to La Roche-sur-Yon, 185km
Monday, 2 July – Stage 3: Cholet to Cholet, 35km (TTT)
Tuesday, 3 July – Stage 4: La Baule > TBA