The hike up to Pas de la Cle is a good one covering 750m of gain over just 4km from Montaud. The pass itself is fairly exposed - which is likley the reason for the warning signs at the bottom - indicating that is is forbidden in high-winds, or during the winter.
The path up to the pass runs to the west of a hunting area, although doesn’t cross into it, however I wouldn’t hang around there too much during November - and don’t act like a wild boar!
Once you get to the path it is a little exposed, but not too bad, and the path is easily visible. There is a little loose rock, but nothing unusually so for the region. A good pair of hiking boots and a little alpine common sense, and you’ll be fine!
Once you get up onto the Vercors plateau, you join the GR9 as the paths tracks the ridge around to La Buffe. Some of the views from this ridge are excellent - and a great place to walk that’s also accessible from within the Vercors.
I wanted to make a circular walk back to Montaud without retracing my steps, so choose to take the tunnel du Mortier through the ridge and back along the abandoned road. The tunnel was created for the 1968 Winter Olympics to provide a way to leave Autrans to the North, rather than having to go South through Villard de Lans. However the soil on the side of the escarpment wasn’t all that stable. The first landslide blocked the road on 30th Jan 1971, which was cleared in Oct 1972. A second slip happened on 20th April 1992 from underneath the summit of La Buffe, and this one closed the road permanently.
It is possible to walk along the road, and drop down to skirt the land-slip, but there is one point that isn’t that stable. Take special care on this section.
The tunnel was interesting, however the road walk back to the village wasn’t the greatest. If you can find a better path down from the face - let me know about it in the comments.
Overall the route was around 16km, with an altitude gain/loss of 1,485m.