In Arith, head to the hamlet of Montagny and then to the end of the road (car park).
(S/E) At the top end of the car park, take the path on the left (towards La Platte - Prépoulain). Pass close to a clearing with a barn in the centre, then head due south until the path begins to descend at a ‘no entry’ sign (elevation 1140 m).
(1) Leave the track and take the path on the right. You will soon reach a sunken track leading to La Platte.
(2) At this point, join the GR® du Tour des Bauges. Follow the wide stony track to the right (heading west), and you will soon reach a fence.
(3) Here you have two options:
Option 1 (the one described on the route map; option 2: see the ‘Practical Information’ section).
If you wish to go to the Curé’s altar after crossing the fence, leave the GR® and take a track on the right heading towards the Chalets Regueras. Behind these chalets, climb up a path diagonally across a slope, then head into the forest until you come to a fence; follow it to the left. From there, it will take a bit of patience and searching to find the altar and the Croix de la Benoîte (the altar is located about 200 m from the Chalets Regueras).
(4) From behind the altar, marked by a red arrow on a tree to the right of the altar, a path leads to the Croix de la Benoîte. To reach the GR®, head north-east across the meadows. The Chambre du Curé cave is located 200 m below Chalet Pernet on the other side of the fence to the right, at the entrance to the small wood. Pass Chalet Pernet and climb to the highest point at 1,438 m; the GR® is just below (thanks to plgrando for the details I’ve added to the description). The route on the map passes by the Autel du Curé.
(6) At the Col de la Cochette, follow the GR® as it climbs towards the viewpoint.
(7) Continue along the GR and leave the Refuge du Creux de Lachat below on your left.
(8) Follow the suggested route carefully as the map does not currently match the actual terrain. Keep following the GR and the signs for Mariet-Dessus / Montagny.
(9) At Mariet-Dessus, the GR branches off to the right towards Montagny. At the wide track, continue to the left, leaving the GR, and you will reach the car park (S/E).