Pilgrims take a small stone or other memento to leave at the base of the monument, Cruz de Fero as a symbol of a burden they carry.
There, I saw many items ranging from stones to wedding rings, photos, a Rubik’s cube, hats, and lots more. I can only guess what each item meant to the pilgrim who left it there. Because so many people carry something significant other than a stone, the monument can look like a dump. For this reason, I recommend carrying only a stone, perhaps with a message written on it.