Mérens-les-Vals, France
Discover the wild sulfurous hot springs tucked into the forest above the old village of Mérens-d'en-Haut, in the French Pyrenees, at about 1,300 meters elevation. There's no built basin here: the roughly 37-40°C water pools naturally among rocks on the mountainside, so you're soaking in a setting that's stayed essentially untouched since a 19th-century plan to build a proper spa station here was never carried through. The site sits on private land accessed by informal tolerance, and it gets crowded on weekends and holidays, so a weekday visit gets you the pools closer to yourself.
The springs are reached by a short, moderately steep uphill walk, roughly 20 minutes from the village lavoir, following the GR10/GR107 path past two houses before entering forest, with wet ground underfoot in the upper stretch. There's no infrastructure, supervision, or amenities of any kind, so pack out everything you bring, down to tissues and cigarette butts, and watch your footing on the rocks around the pools. It's free to visit and technically accessible year-round, though May through October is the recommended window. Anyone with heart conditions, high blood pressure, circulation problems, open wounds, or who is pregnant should check with a doctor before getting in, and don't expect any staff on site if something goes wrong.
