
At the foot of the Plan d’Acier’s high cliffs is the Bienne, imprisoned in this boxed-in location in the valley by the Étables dam. Since 1932, when it was first put to use, this dam has fed the electrical plant in Porte Sachet through a penstock pipe dug under the Truffet, the strange sugar loaf that overlooks one of the Bienne’s bends.