Emile Zola 
Lourdes The Three Cities Trilogy 

In this moving depiction of a pilgrimage to Lourdes, the master French realist has created a novel of vivid characters and subtle commentary on suffering and the belief in miracles as the last desperate refuge from pain. Based on his own trip to the fabled grotto, the novel follows a simple five-part structure corresponding to the five-day train trip from Paris to Lourdes and back. (Goodreads)