Clean Means in the Pyrénées

Surrounded by snowcapped mountains, sun worshipers and scientists have begun to flock to the Cerdagne Plateau, where clear skies and a high altitude provide the most intense sunlight in all of Europe. These unique solar conditions have attracted several cutting-edge solar research centers, including Thémis, which opened its doors to the public in 2014. Here you can test solar prototypes like solar-electric go-karts and peruse interactive sun-centered exhibits. The plateau is also home to Odeillo (www.pyrenees-cerdagne.com/decouvrir/les-sites-solaires), the world's largest solar furnace, which produces temperatures up to 6,330 °F. Tour this solar oven in the town of Font Romeu, or see a smaller model in the fortified town of Mont-Louis.

To reach these sunny heights, use the 100-year-old le Petit Train Jaune (www.pyrenees-cerdagne.com/decouvrir/le-train-jaune), aka the Little Yellow Train, which is powered by hydro-electric generators. It chugs up to France's highest train station, passing through 19 tunnels and crossing two viaducts, one a suspension bridge over a heart-pounding precipice. If you plan to stay a night or two, check out the solar-powered eco-lodge, L'Orri de Planès (www.orrideplanes.com)–-you get a discount if you arrive on foot, bicycle, bus, or train–-or the mountains-to-Mediterranean sea–bike tour with Real Travel France (realtravelfrance.com).