Mind numbing? No. Certainly not as bad as the Portsmouth one used to be. 36hrs!
Not long back from Spain on the bike. Plymouth to Santander, Bilbao - Portsmouth. Now both 24hrs with Brittany Ferries.
Arrive in Santander, Picos D'Europa west, along some brilliant m/way. East for Pyrenees again along some awesome m/way. Spoilt for choice. No hours and hours of dull peage through France. Instant goodness!
Usually head for Jaca as a first stop. Plenty of accom.
Only road you need to know is n260 for Pyrenees.
Gets you to the beaches eventually. Cadaques is beautiful.
Barcelona - Santander back is a (long) days ride on the m/way. Have stopped in Zaragoza a coupla times to break it up. Very very nice. Very very hot too(105f a few weeks ago.)
But you miss out on gems like any of the roads north/north west from Soria. N111 (don't go through the new tunnel, take the "high road") or even better Sierra De La Demanda. LR113.
Peak of N111. Nobody there whole road up and down. Bliss.
Picos
