Camino de Besaya/Pisuerga
Santillana, Aguilar de Campoo, Carrión de los Condes
The route from the Camino de la Costa at Santander/Santillana to the Camino Francés at Carrión de los Condes is described on various sites, including the Cantabrian government. This is mainly aimed at motorists, but the route from Santillana to Herrera del Pisuerga based on the Roman road is being developed as the GR73 Calzada de los Blendios; see here, here and here; Herrera can easily be linked with the Camino Francés at Frómista via the Canal de Castilla.
Id: besaya