The trailhead is located at the entrance of the Vallon de They, just past the Morgins Ranch.

The itinerary offers nine interpretive panels along the route through the They Valley, between Morgins and the Col des Portes du Soleil.

Walking upriver to the source of the Vièze, you’ll see that the water changes colour; alternately red, blue, yellow, white, and green! The panels provide geological, hydrological, and hydrogeological explanations as to why the colours change so strikingly, how water and minerals interact, how water can suddenly disappear or appear out of nowhere, and why these mountains are so uniquely special.

Keep your eyes peeled for:
- Red at the Eau Rouge Spring
- Blue at the edge of the Vièze River
- Yellow at the Fontaines Jaunes
- White at the Fontaines Blanches
- Green at the Lac Vert

You'll find alpine restaurants along the way - the Chésery Hut at Lac Vert, or the Tovassière and They 'Cantines' in the They Valley.
Marking : At the Lac Vert (Refuge de Chésery) please follow the diversion that has been put in place: take the wide path to the left of the lake and not the small path to the right, which is closed for works during the summer of 2023.
Equipments : Picnic area,