Check any “Top 10” list of best world hikes and the GR20 is on it. Check any “Top 5” list for most difficult hikes and the GR20 will be there. While the GR20 in Corsica probably earns its reputation as Europe’s most challenging hike (saw several young and fit guys quit), I wouldn’t put it on the top of your list. There are much prettier hikes in Europe to challenge yourself on. Unless you simply want to check it off your list or are looking to challenge your fitness, head to the Alps or the Scandinavian countries.
The “trail” is almost entirely climbing up and down rocky, scree filled mountain passes (~25,000 ft total in north section), following painted markers on the rocks. The ground underfoot is rough and the climbs are steep, requiring scrambling, rock hopping and a bit of climbing with chains. On top of this you are almost always exposed and hiking in the 90 degree sun. So, if you are accustomed to hiking on AZ, par for the course, but it is less pretty than AZ and non-stop rough.
I may be slightly biased here because it reminded me of hiking in AZ and I was hoping for something more exotic. Because of this, after finishing the hard part (north section), I left with some trail mates for the beach (Corsica’s villages and beaches are GORGEOUS!!! and I highly recommend).
The Ragamuffin Billy Goat 