From the N19, now known as the D619, head towards Étobon via the D127.
Park in the car park on the right-hand side of the road, about 500 m after the previous junction.
(S/E) The start of the walk is marked by the Yellow Ring sign. After a long descent, pass over the lock, then keep to the left and reach a cross-track after the lock bridge.
(1) At the end of the bridge, turn left and walk alongside the Étang Déchaudey. Next, a section of the canal that is not very visible leads up to the road (D127).
(2) Cross the road and take the path directly opposite, leading you to one of the ventilation shafts for the tunnel.
(3) Continue down the path to a bridge spanning the canal.
(4) Cross the bridge, then, a few metres further on, turn left and continue until you reach a wide track.
(5) Follow it until you reach the road (D127), then follow the road to the left to return to the nearby car park (S/E).
A fairly easy hike with a few ascents and descents in a magnificent forest. We did this hike in winter, which gave it a very special atmosphere. We'll be going back this summer to compare!