We are doing the Best of the Basque RS tour and are wondering whether to stay an extra night or two in Bilbao or Bayonne? Thanks
Both tours include 2 nights (and a full day) in each location. Perhaps some time further along Spain's northern coast to Santander and Santillana del Mar in Cantabria.
http://www.spain.info/en/que-quieres/ciudades-pueblos/otros-destinos/santander.html
http://santanderspain.info/en/
http://www.spain.info/en/que-quieres/ciudades-pueblos/otros-destinos/santillana.html
http://www.santillana-del-mar.com/english/index-i.htm