It's moto, but I think the consequences of a mistake are much more severe. The "trail" is a pass between Italy and Austria that was used to transport people/supplies undetected during WW II.http://www.collegehumor.com/video:1930833
I'd jump at the chance to ride that (the Italian one), although I'd pick a trials bike over an enduro bike given the choice. There's a fair amount of this sort of stuff in Greece too, or anywhere else with proper mountains I suppose.
Anyway, the trail along the side of the Koskarakos gorge is on my doorstep (well, 30 minutes away) and one that I ride now and again. The photograph doesn't do it justice but the drop to the bottom is around 350 feet at that point and the path is in places less than a metre wide.
The Val D'Uina is probably the best known of these old routes and one that I always promised myself that I'd ride, after seeing some film footage of Hans Rey riding there.
It seems increasing unlikely that I ever will however, even though it was on my list of must-ride places.