Start at Marnans: head for Saint-Etienne-de-Saint-Geoirs, past the factory, then Château de Bressieux.
Continue on the D130B and turn left towards Combe de Vaux.
After Saint-Étienne-de-Saint-Geoirs, head for Saint-Geoirs-la-Barrière. Carry on to Izeaux via Plan.
When you arrive in Izeaux, head down towards to La Forteresse on the F73B towards Saint-Paul-d'Izeaux and Girin.
Continue towards Saint-Michel-de-Saint-Geoirs via les Fourcoules, then follow the Toutes Aures pass via Brion.
Finally, head for Roybon on the D156 and turn right on to the D156C towards Marmans and your starting point.
Good plans : Chambaran mushrooms: Chambaran forest is famous for its mushrooms, especially around the Col de Toutes Aures. Main species include penny buns, horns of plenty, chanterelles and grey chanterelles. Of course, the best season is autumn, but some mushrooms grow earlier, such as the summer cep, which grows under oak and beech trees from June to September. Nicolas Grandclaude, chef at Atelier Grandclaude in Marnans, is a big fan: "I love walking in Chambaran forest foraging for mushrooms. And I can serve them in my restaurant regularly, because I'm lucky enough to know gatherers who sell me their find. I use them in a range of recipes such as cream of mushroom soup, small biscuits and pan-fried penny bun mushrooms with parmesan and gravy. They give earthy flavours that are a regular feature of my autumn menu ".

Admission fee : Free access.

Opening : From 01/05 to 31/10. Subject to favorable weather.

Area : Bièvre Isère