France; Circular mtb trails like eg Marin/Penmachno

Thinking of seeing France probably 3 or 4 weeks at 3 or 4 gites in different parts of the country April 2012. Will be with with wife & dog neither of whom cycle. Would be good if anyone knows starting point of ,say approx 3hr circular trails that I could do while wife reads/walks the dog. Something like Marin trail or Penmachno would be ideal (or dont they have those sorts of waymarked trails in France?) Any suggestions appreciated.