Most people have already heard of the Santiago de Compostela ( St-James way ) pilgrimage : it's a classic. He has the merit aside from his age (he was born in the 9th century AD), to be easy on physical point of view, easy to refuel in food, frequented and well marked.
For a first long trip it is the ideal !! That was the case for me in 2016, I let you discover right now, in image 6 months and 1 031 miles on this path.