Circular route via Corne Bœuf and Lac d'Armaille from Thoys

From Belley, head towards Saint-Germain-des-Paroisses (CD 41) and, before climbing the first slopes of the Jura, turn left onto the CD 10d towards Arbignieu and stop at the hamlet of Thoys.
Coming from the south along the Rhône, after Peyrieu, leave the CD 10 at the Forêt de Rothonne on the left towards Peysieu, then immediately (after 300m) turn right onto the CD 10d, pass at the foot of Arbignieu for the hamlet of Thoys.
From Glandieu and Prémezel, pass through Peysieu and join the previous route.
In Thoys, there are only three parking spaces near the wash house. If they are taken, return south to the Chemin du Moulin junction where there are several parking options.

(S/E) From the centre of the hamlet (wash house), take the road south for 400 m and, just after crossing the Ruisseau d'Armaille, turn right onto Chemin du Moulin, to the foot of the hill (old mill).

(1) Take the path opposite that climbs to the left and, at the next junction, turn right to return to the Armaille stream.
Do not cross it, but follow its right bank westwards, along a fence. The path then climbs to the left and joins a track that goes up a long gully at the foot of small cliffs, at Le Balai. At the top of the valley, the path descends a little and continues south-west, gradually leaving the forest and reaching a major crossroads marked Bagne.

(2) Turn right to cross northwards to another major crossroads. Take the second path on the left, which quickly joins the Roche Percée trail, going left and back.

(3) From the Corne Bœuf passage, return to the main trail and take it north. It descends towards a marsh that is often submerged, which it follows to its northern end, where you can admire it in its entirety.

(4) Return to the main path heading north, which passes a threshold and descends to a crossroads where the path on the right leads down to the ford on the Ruisseau d'Armaille, flanked by a rebuilt footbridge.

(5) Cross and continue straight ahead to reach a building on the edge of Lac d'Armaille.

(6) Take the path northwards, which passes a threshold before reaching the CD 41 (Saint Germain-des-Paroisses road).

(7) Turn right along the road and after 100 m, descend to the right onto the path that cuts across the road, which it joins. Follow it to the right and just after a bend, leave it again for the path that cuts across the bend in the road and descends to a crossroads shortly before returning to the road.

(8) Take the forest path to the right (south), which climbs slightly to a threshold, then veers left (east) and then south again to descend steadily through the forest to the foot of the hill, where the path turns left and joins the CD 10d at the Mutin crossroads.

(9) Turn right (south) to return to the hamlet of Thoys (S/E).

The entire circular route is marked (yellow) with directional signs at the main crossroads.
Only short return trips are not marked.

The marshes and lakes have very variable water levels depending on the season, which can make passage difficult in the event of high water: along the Ruisseau d'Armaille, near the ford and along the lake.

If the footbridge is unavailable (it has been washed away in the past), there is a detour downstream: a path allows you to cross the stream in a rocky section, via a small metal plate placed over a narrow section.

Alternative route: to cross Corne Bœuf, at the junction before the WP (3), take the first path on the left, which crosses level clearings, and just before a junction of carriage roads, turn right onto a discreet path that enters the boxwood trees and joins the foot of the La Roche Percée passage.

This route is mainly through forest, pleasant in summer and autumn, but passable in all seasons.
As a result, it offers few unobstructed views, limited to the nearby peaks of Bugey, Mont du Chat and, in good weather, La Tournette.

The Roche Percée de Corne Bœuf passage is easily crossed via a path: be sure to take the correct path that runs through it.