There are entire books around it but I’ll try to sum it up for you.
Santiago de Compostela it’s one of the most famous places for Christian pilgrims(along with Jerusalem and Rome) because it’s said to host the remains of the apostle St Jacob (also named San Tiago, Saint James, Saint Jaques, Sfantul Iacob).
It’s similar to how the St Peter Cathedral in Rome hosts the remains of the apostle Saint Peter.
The legend (how I understood it yet) says that St Jacob came to west Europe to spread Jesus’s words, along with his disciples. He returned then to Israel where was killed, but his disciples took his body back to the Iberic peninsula where he preached and buried it somewhere in Galicia, Spain.
The location wasn’t known up until around the 9th century when a shepherd found the remains in a field in the town of Iria Flavia (today is called Padron) and said he might have found St Jacob’s grave. The king at the time (Alfonso 2nd) heard the news and asked the pope to confirm if the news are true. We need to also be aware that was a period where wars were taken in the name of religion. So this would’ve given Spain an immense reputation.
The Catholic church confirmed the remains are indeed Jacob’s. The king then decided to make himself the first pilgrimage journey from the Spain capital (Oviedo, at the time), to that small town where he build initially a chapel. He later commissioned a larger cathedral dedicated to St. Jacob in Santiago de Compostela, to attract pilgrims from all over the world.
The people started indeed to come to Santiago to pray to St Jacob’s relics, becoming pilgrims doing El Camino de Santiago (the way to Santiago).
While for a long time this route was done for religious purposes, now people are doing it mainly for 3 reasons (religious, spiritual – I would argue it’s the most frequent reason, and touristic reasons).
As a short personal opinion, the journey is mostly famous because it transforms the people. Every single person I know and who did it keeps a strong memory about it in their hearts. It’s something magic about the journey, the struggle, the stories that are shared, the feeling of accomplishment at the end, and the connections made – with other souls, with nature, with God, or the Universe.
It is indeed, one of a kind.
*all photos have been taken on January 2022