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From Erigné (1186m) or Charny (1273m), take the trail that traverses to pont de Chardonnière (1309m). Follow the torrent via one or the other bank and pass the Chardonnière country cottages (1346m). Continue by skirting the Terres Maudites towards the east, in the direction of the Bretolet pass. Slightly before the end of the dale, overtake a small scoop on the right where several corridors emerge including Pas de la Latte, on the left bank, (walkway in summer) and la Virgule, on the right bank, which starts with a small very narrow and very boxed in corridor, facing W. You come out of the corridor to overtake a rather steep and now very exposed slope (rock barriers at the base). Go primarily to the left (E) to go up to the base of la Virgule: ice gully in a circle arc bordered on the left by a rocky vertical muraille even overhanging and on the right by immense rock slabs, not very broad but less exposed and less steep. Go completely up this ice gully and around 2250m you pass a striation in the muraille overlooking on Switzerland, Brêche de Roland style: la Fenêtre des Chamois. From there the slopes are less steep and it is easier to reach Bossetan summit (2406m) via the N ridge resulting from the above muraille.
Descent by the same route or directly in the large slabs if the snow conditions are optimum.