Shortly after the start in Ballaigues, the route crosses the motorway and, a little later, the Lac du Day dam which stores water from the river Orbe. This river has its source in the Grotte de l’Orbe, a stalactite and stalagmite cave that is one of Vallorbe's tourist attractions. The path takes you past Le Day Viaduct, a fine stone arch bridge dating from 1925. Walk along the shore of Lac du Day reservoir until you reach the Iron and Railway Museum. Since the Middle Ages, Vallorbe's deposits of iron ore and reserves of firewood have helped it to develop into a major centre of the iron industry.

Hemmed in between the Dent de Vaulion and the Mont d’Or, the path leads to the venerable station building at Vallorbe. However, the size of this railway station is not due to the town's population: it was needed because the routes between Lausanne, Yverdon and France were historically important. The border with France also lent the town in the Vaud Jura strategic importance and made it a transport hub. Our route out of the centre of Vallorbe leads across the river Orbe. A long gravel track runs uphill through the forest, becoming a steep path just before La Mâche. With the first 400 metres of altitude overcome, hikers enjoy a beautiful view of the neighbouring mountain and the day’s destination.

Passing over meadows and a short ridge section, the trail reaches the Dent de Vaulion about an hour later. The region’s highest peak has the whole of western Switzerland at its feet. On a clear day, there are no fewer than eight lakes to admire, most notably the Lac de Joux and Lac de Brenet in the Vallée de Joux. Crossing another meadow, we hike downhill to the restaurant before the varied trail runs through the forest to Pétra Félix. It passes by old tank traps and bunkers to reach the shore of Lac de Joux in Le Pont about half an hour later. The water from the two lakes runs off underground, forming the karst cave and tourist attraction of the Grottes de l’Orbe near Vallorbe.