Brierley’s guide shows three routes into Burgos but the signage is not good. It certainly wasn’t good on the “green” river route I took. I followed instructions provided on the Camino forum. I’m going to rephrase them below based on my walk a couple of days ago.
1. Follow the yellow arrows on leaving Orbaneja Riopico.
2. Cross bridge over highway and see the decision point at the first building. A camino sign points straight (rightish) but this must be for the grey/asphalt route. Both other routes go through Castanares, so you should take an immediate left. The path will wrap around the Burgos airport and eventually get to the village of Castanares.
3. When you reach the main road in Castanares, cross immediately and go straight ahead. (Don’t follow the main street to the right, as indicated on some arrows I saw. Those arrows might be for the “middle” route along the N-120.)
4. Continue straight, passing a children’s playground. When you reach the factory you’ll have to turn to the right.
5. Passing by the factory, on the left you will see a footbridge. Walk across this bridge and the path then goes to the right, parallel to a highway (which is on your left).
6. Continue until you come to an underpass below the highway. It is not a fancy underpass, but go under the highway and you enter a big recreational area.
7. This recreational area follows the Rio Arlanzon to the Centre of Burgos and beyond. There are many trails and paths. It doesn’t matter much which path you take as long as you follow the river and don’t stray too far.
8. It is still quite a long walk! There are several footbridges across to the city on the right. Wait until you have passed the third motor-vehicle bridge before crossing. Just after the third bridge you will see the Museum of Evolution on your left. It is a large new glass structure.