Travelling in Spain

My husband and I would love to travel through spain June 2015. I have searched the internet for suitable routes to cycle as we would like to do at least 2000 Km . We would however like to cycle on quiet roads, but having a hard time trying to find a suitable route. I have read about the old railway lines not being used but have no idea where to start. I would appreciate any suggestions , We travel on bikes with our panniers. THe only route I find that is complete seems to be the Way of St James? please assist as I am getting quite worried as we have only 4 months to plan.