Not sure if it counts as off road - it's definitely not asphalt - but most of the bloody roads in Portugal are made of cobblestones!

True, but seriously I'd look into tracks in Portugal at that time of the year, aswell as southern Spain as others have mentioned

The Peloponese peninsular in S. Greece is a lovely part of the world as well. I was there once in the spring when flowers bloomed everywhere... magic!