The route starts from the Passo del Lucomagno and heads along a flat dirt road to Alpe Croce. The trail winds through flat pastures on the right side of the valley and reaches Foppa di Pertusio before descending to Alpe Casaccia, crossing the Brenno river.

It then climbs along the left side and continues toward Alpe Pertusio on a flat path along the river which, on sunny days, takes on wonderful shades of light blue, often with small white sandy coves.

It is a very picturesque river section: the river, with its successive winding curves, creates a unique riverbed that generates a unique ecosystem after each flood.

In the water, besides the trout, there are hundreds of insect species, such as mayflies, stoneflies, and "stone carriers." Life also continues beneath the visible parts: even in the sediments under the gravel, for several meters deep, tiny aquatic organisms can be found.

At one point, you reach a sign indicating the source of the Brenno river, reachable within a few minutes.

Upon arrival, a truly wonderful spectacle awaits: water flowing clear and pure directly from a crevice at the foot of the mountain. With a maximum flow of 1,300 l/s, it is one of the largest in the canton: two divers managed to explore it for 300 meters, reaching a depth of 45 meters!

The trail then immediately ascends northward, passing through a very short, quite steep section, before reaching the starting point along the wide meadows of Passo del Lucomagno.