When you walk any of the Camino long distance walks in Spain you need a passport.
Its known as The Credencial del Peregrino.
The Credencial del Peregrino, is a sort of pilgrim passport that is stamped along the way and serves as proof at Santiago that you have indeed followed the pilgrim route and deserve a Compostela.
The Compostela is the certificate awarded at the end of the journey.
The passport is also required if one intends to stay at any of the refuges along the camino .
Alas mine only has 6 stamps……. so no Compostela for me just yet 🙂