Les Bains de Lavey

Les Bains de Lavey holds the double distinction of being Switzerland's oldest spa and the source of its hottest natural thermal water. A stream of hot water was discovered in the bed of the Rhône in 1829, prompting geologist and engineer Jean de Charpentier to investigate for the Vaud cantonal government, which purchased land to develop permanent bathing facilities from 1833 onward. The sodium-chloride saline water originates high in the massifs of the Dents du Midi, Tour Sallière and Émosson, descending through crystalline rock fissures roughly 3,000 meters beneath the Rhône Valley, where it reaches around 120°C, before rising back to the surface at Lavey through a separate fissure network at up to 62°C. Carbon-14 dating shows the underground journey takes somewhere between 5,000 and 10,000 years, making Lavey's thermal water some of the oldest groundwater used therapeutically in Europe.