FATMAP difficulty grade
From top of Marmotte III go on the Cristaux slope and do a long traverse to the right (you have to stay quite high up.) You will always find tracks here as the route is very popular and it's accessible to all levels of skiers provided you're competent off-piste.
The skiing follows a pleasant combe and then rejoins the Sarenne piste.
From the Sarenne slope you can reach Alpe d'Huez with the Chalvet lift or the Alp'Auris.