From the N19, now renamed the D619, head towards Etobon on the D127.
Park in the car park on the right-hand side of the road, about 500 metres after the previous crossroads.
(S/E) The start of the hike is marked by yellow circles. After a long descent, pass over the lock.
(1) At the end of the lock bridge, turn left and walk along the Etang Déchaudey. Then, a barely visible section of the canal precedes the climb up to the D127.
(2) Cross it and take the path directly opposite. Pass close to one of the wells used to ventilate the tunnel.
(3) Go down to a bridge over the canal.
(4) Do not cross it, but take the towpath on the left, marked with yellow triangles. Reach the tunnel entrance.
(5) Above the tunnel entrance, turn right. You will soon come to a wide track; take it to the left. You will reach the 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!