The Camino exists because a tomb found in Galicia in the ninth century, in the reign of Alfonso II, has been venerated ever since as that of St. James the Greater. Pope Leo XIII declared the relics in the cathedral to be his in the bull Deus Omnipotens of 1884. Pilgrims have walked there for more than a thousand years, and monasteries and churches grew up along the way to serve them.
No one checks your religion on the road. The pilgrim credential, in the cathedral's own words, is for those who make the journey with a Christian sentiment or with an attitude of search, and it is all a pilgrim hostel asks to see. At the end, the Compostela is reserved for those who come to the Apostle's tomb for religious or spiritual reasons; you state your motive when you register, and it is a matter for your own honesty. American Pilgrims on the Camino lists the reasons people give: faith, a challenge, health, history, nature and companionship.
At the cathedral the Pilgrim's Mass is offered daily at the main altar at 7:30 am, 9:30 am, noon and 7:30 pm, and there is Mass in English at 10:30 am in the chapel of the Pilgrim's Reception Office every day except Wednesday (times checked October 10, 2026). A visitor who is not Catholic is welcome to attend and to pray. Holy Communion is received by Catholics; the U.S. bishops' guidelines welcome other Christians and people of other faiths to the celebration and ask them not to receive, but to join in prayer for unity and peace.
Good to know before you go: backpacks are not allowed inside the cathedral, so leave yours at your lodging first. Catholics who walk will find what the route was made for: Mass and confession at the end, churches along the way and time to pray. If you are simply curious, the Camino is a good place to see the faith lived at walking pace.