Expatriate Norwegian Ivar Rekve, who consults to the Pilgrimage Office in the city, says that the vast majority of pilgrims cite spiritual motivations for doing the walk, even if they are not specifically Christian.
"Some people say that they have found themselves at a crossroads in their life and are wondering where to go next," he says.
"Others may have lost a spouse or a loved one or recovered from life-threatening illness. Very few people take it on just as a hike."
A visitor to Santiago de Compostela can scarcely avoid seeing the pilgrims: they arrive, often limping on blistered feet, at the rate of about one a minute (on the day of writing, 852 had completed their walks) and they gather around dusk in the huge square in front of the cathedral for an official welcome. More than a few tears are shed - though whether they are tears of pious joy or gratitude that the long slog is over is not always easy to tell.
In fact, there are more than 100 pilgrimage routes. The most popular by far, the Camino Frances, or French Way, starts on the French side of the Pyrenees and, from the Spanish border, runs about 750km - a stiff 30-day walk - to Santiago. But others snake through central Spain, or up the Portuguese coast: all roads lead to the cathedral.
Along the way, you get stamps in a credencial or passport to prove you passed that way. And at the end, provided you have walked a minimum 100km, you get the certificate of achievement known as the compostela.
Walkers don't need to book - although getting a bunk in one of the €5 ($9) albergues along the route can be tricky in high season. But increasing numbers of New Zealanders are taking an interest: Rekve reports that 138 Kiwis made the walk in 2006 and 200 last year.
Useful sites:
csj.org.uk
peregrinossantiago.es