From Paris : A6 to Dijon, then A36 to Poligny, follow N5 direction Geneva, at "Pont de la chaux" turn left and follow the direction of Mouthe, on 12 km ; reach "Foncine le haut", then 2 km on D437, turn right after the sign "Castel Blanc"
from Lyon : N36 to Bourg, Lons le saunier, Champagnole then N5 and follow as befor.
From Switzerland :
Highway to Vallorbe, then 30km on D437
or by the Vallée de Joux, to Mouthe then 8km on D437