I walked this trail a couple of years ago with Peregrina2000, who may well have written up her trail notes somewhere on this forum -- worth a search! It's marked as Camino St. Olav, with stylized red cross logos -- Don't expect yellow arrows. You will definitely need a good map (or GPS tracks) and a mobile phone, as the trail and available lodgings don't always come together perfectly.
This is Castilla Profunda.
Terrain can be rugged, trail markings sparse; some etapas are pretty long without shade or good places to stop and rest. But it DOES have a cool set of dinosaur footprints, Spain's second-oldest church, Grammy-winning Gregorian chant, a fuente built with Visigothic stone sarcofagi, great big blue skies, and spectacular views over valleys filled with massive herds of sheep.
The final day follows an abandoned railway, it's buzzing with bikers and day-hikers, lots of fun energy right on into Burgos.