Fearless intermediates can enjoy this really long black run from the top of Alpe d'Huez and there are two ways that you can approach this spectacular run:
The Sarenne
As it should be done
Access to the Sarenne is simply found by passing the Tunnel entrance and continuing as far as you can go. You have to deal with the black piste that precedes the Tunnel, which is not as daunting as its grading suggests. The run then continues for an estimated 17km and is not really black in terms of difficulty, it actually alternates between blue and affable red until it enters the Sarenne Gorge, when it rather fizzles out into a 5km flat path.
Where it distinguishes itself is that the scenery is stunning, the run is undoubtedly long and you ski a non-stop vertical descent of nearly 2,000m in an undeveloped area of mountain.
The reason that the Sarenne is rated black is partly because there is a wide steep 'nearly' black section at the top, but mostly because once a skier has started the run it's not possible to turn back.
Alternative run
By taking the Marmotte III lift you can ski a couple of chairlift-served, very high altitude red and blue runs that liaise at the bottom with the Sarenne run and therefore miss out the black aspect of the Sarenne. There is no run back from the Marmotte III lift that will return you to Alpe d’Huez other than via the Sarenne.