From Arêches, take the D218d towards Lac de Saint-Guérin.
(S/E) From the car park near Lac de Saint-Guérin, take the small road that descends towards the dam arch. Cross it and continue along the wide path that runs alongside the lake.
(1) At the end of the lake, you will come to an intersection. Turn right and head west at the start, following the marked trail (directional pole) leading to the Rognoux chalets.
(2) You will reach a fork at the mountain pastures. Follow the yellow-marked path to the left, heading west, which leads to the Rognoux chalets and passes close to the Rognoux ski lift. Ignore the various paths that cross the trail.
(3) You will reach a three-way junction. Continue to the left, following the path without leaving it. Follow the yellow markings towards the south-west, towards the Col de la Forclaz. Pass close to the Col de la Forclaz ski lift and to the right of Grand Rognoux. Continue to the Col de la Forclaz.
(4) Caution: from this pass, behind which the summit of Grand Mont with its antennas can be seen, you must be careful and vigilant about your direction: the trail, which is more or less well marked in yellow (also marked with numerous cairns), continues to climb along the ridge line, in a very mineral world of large boulders and pebbles.
(5) Continue climbing straight ahead. Ignore the path climbing up from the Col de la Louze on the left. Some snowfields, which can be quite large, may hide the markings, so follow the cairns carefully to get around them if necessary. You will see the summit of Grand Mont ahead of you.
(6) Descend via the same route to the lake (S/E).
For an alternative descent route, see the practical information.