While this hike takes you to the largest alder forest in Europe, it first and foremost cristallises men’s fight against erosion, with embankments and dams built to protect against flooding. It also crosses a forest with various tree species (larch, pine trees and spruces), the result of a sustained effort over a number of years by forestry workers to retain the soil since the end of the 19th century. From Col d’Ornon , follow the signposts Cabanes des Roudons , via Entrée du Col, Le Vernay, Bois du Vernay, Les Palles and Les Roudons . At Les Roudons , you have the option to go all the way to the cabin (please respect the place), or take the return path by following Les Adreys, Le Crozet, Côte Plane . Then follow Col d’Ornon , via Les Siauds, Les Suffets, Le Pied du Vernay, Le Vernay and Entrée du Col .