To get there, you park in a place called le hameau des Clots, then walk up a meandering trail that takes you past a shepherd's house and then high up into the valley. After two hours of walking up, you reach the start of the climb at the base of the mountain's west face.
You can get to the top in four pitches, about 120 meters of vertical climbing, then walk the narrow ridge to the summit. Just past the summit, and at the southern end of the rock, you can rappel down (15 meters) to a hard-sloping, zig-zagging trail that takes you back down the valley.
Guidebooks claim that the Gerbier constitutes an excellent introduction to mountain climbing. It's not for the beginning climber, however. Or anyone afflicted with vertigo.
These photos are courtesy of Laurent Fondacci, the guy who brought me up and back down the Gerbier...safely. Thanks Laurent!
The south-west face of the Gerbier in the morning light.
The slope leading up to the base - west-face.
The start of the climb. You can see two climbers
already on the rock, about 3/4 of the way up.
Laurent leading us to the summit. It was late August but cold
and windy enough to wear polar fleece and Gore-Tex jackets.
Enjoying the view from the top.