Of course, the most traditional way to arrive in Santiago de Compostela is by foot, following the traditional trail of Saint James:
Its main branch or “French Trail” starts in Paris. From Notre Dame, cross the Seine through the Petit Pont, and follow the Rue Saint Jacques (of course) southwards. Eventually you will reach the town of Saint Jean de Pied de Port, at the Pyrenees. Continue to Roncesvalles and then turn west to Santiago. The trail takes about 30 days from Paris to Roncesvalles and 30 days from Roncesvalles to Santiago.
Alternatively, Lavacolla, where the Santiago airport is located, is right on the trail. This is what the French medieval traveler Aymeric Picaud wrote about Lavacolla in his “XII century Guide du Routard” (the Codex Calixtinus): “Among the rivers with sweet and healthy water to drink, the Lavacolla stands out, because at a shady spot which it crosses, two miles away from Santiago, pilgrims of the French nation walking towards the city, strip off their clothes and for love of the Apostle wash, not just their private parts, but the filth of their entire bodies”. So once you get off the plane, you can walk its last 10 kms to Santiago and enter the city like a real pilgrim. If you prefer, you can rest first at some of the hotels located near the airport and take the walk in the morning.