From the northeastern side of the Colle del Lys parking area, take the wide gravel road that gently descends into the Colle del Lys Natural Park, skirting the northwestern slopes of Mount Arpone. From the very start, excellent views open up towards the Gran Paradiso massif.

The track winds downhill through woodlands dominated by birch and larch trees, crossing several block streams typical of this area—dark accumulations of broken rock that bear witness to the ancient oceanic origins of the underlying geological formations. Openings among the trees provide broad views of the Civrari massif, the Gran Paradiso range and the Richiaglio valley, a branch of the Viù Valley.

Upon reaching the lowest point of the route (1,222 m), the road begins climbing again, passing several picnic tables and benches. After a few gentle ups and downs, you arrive at Barlot Fountain (1,230 m).

Leave the gravel road here (you will return to it later) and take the mule track that climbs to the right through a dense forest of beech and pine trees. A series of switchbacks leads to Portia Pass (1,322 m), the watershed overlooking the Casternone Valley, where the refuge of the same name stands. Despite its name, this is not a staffed mountain hut but a simple emergency shelter. Since it replaced an old wayside shrine, it is still commonly known as “Cappella Portia” (Portia Chapel).

Take the path that climbs steeply to the left, entering a small woodland. Continue along the mountainside above the Casternone Valley, traversing several stretches of rough rocky ground. As compensation for the uneven footing, the route offers fine views of nearby Mount Musinè.

Suddenly, the trail emerges onto a grassy clearing dotted with birch trees, marking the highest point of the entire itinerary (1,416 m). Ignore the branch leading to Il Pilone and descend to the right, crossing further rocky sections. The trail then continues on a gentle descending traverse, passing near the wooden chalet of the Lunella guesthouse, which remains slightly below the path.

The route crosses beautiful meadows with magnificent views of the Gran Paradiso range, skirts a small hillock on the left and then bends right towards nearby Lunella Pass (1,372 m), which, like Portia Pass, marks the watershed with the Casternone Valley.

Continue left in the direction of Mount Colombano. After a short distance (waymarker), turn left again and follow a long contouring traverse along its slopes. Cross additional scree deposits, pass a water intake structure and reach the attractive hamlet of Giuglitera (1,344 m), where a gravel road is encountered (you will return along it later).

Remain on the trail, crossing further rocky sections until reaching Grisoni Pass (1,398 m), the watershed overlooking the Rio delle Toglie valley, a tributary of the lower Viù Valley.

On 23 September 1944, a group of Nazi-Fascist troops, concealed by extremely dense fog, advanced up the Rio delle Toglie valley and crossed Grisoni Pass, taking a partisan detachment by surprise. The partisans managed to withdraw towards Colle del Lys without casualties, but their mountain huts were burned down and the group was forced to relocate to the lower Susa Valley.

Ignore the trail descending into the Rio delle Toglie valley and follow a grassy track heading southwest. Although not particularly obvious, it is marked with paint blazes and cairns and descends towards a gravel road.

Follow the road to the left and, after several short ascents and descents, return to the houses of Giuglitera. A little farther on, at a junction, descend to the right. At a hairpin bend (1,270 m), before crossing a stream, leave the main road and turn left onto a secondary track which follows a shorter route before rejoining the road lower down (1,214 m).

Continue left along the well-surfaced lane, which first runs almost level and then climbs gently back to Barlot Fountain. Having completed the loop, simply retrace your steps to return to Colle del Lys.

In the square at Colle del Lys stands an imposing circular brick tower, nearly eight metres high and faced with exposed river stones. The monument commemorates the more than two thousand partisans who lost their lives in the Lanzo, Susa, Sangone and Chisone valleys. A visit to the Resistance Ecomuseum is highly recommended, as it documents and preserves the memory of the partisan struggle that took place throughout these mountains.