I'm doing a similar thing and travelling back from Fromista to Burgos ( in August)- the local bus is cheap and takes about 1hr 30mins. I think there is an ALSA long-distance bus from Burgos to Santander.I live in Madrid and one thing to be aware of is that some local bus services in Spain have...
I am walking from Pamplona for about a week from 27 November - unfortunately I can't get away for the period of a whole camino so I will be doing it in chunks, at different times.
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