was just curious, and it seems to be a walking trail, but here is a link to some people who biked part of it

https://gypsybytrade.wordpress.com/tag/cycling-the-gr5/

as a walking trail, this may explain how I briefly read in the links blurb of how it was sometimes hard following the trail.

Im sure you have heard of the various Eurovelo bike routes, but look into them if you havent. I know one of them goes from Switzerland up the Rhine to Holland. Lots of info about them all, easy to find.