In one of his final official acts before he died, Pope Francis put Antoni Gaudí, Spain’s most famous architect, onto the path to sainthood. Gaudí's masterpiece, the Sagrada Familia, is a towering basilica, strangely designed and bursting with colour. It stands in the heart of Barcelona and its walls recount the entire story of the Catholic religion. After 140 years, having survived wars, arson attacks and dictatorship, it is still under construction. As Gaudí worked on it throughout his life, he became obsessive and it intensified his devotion. By the end of his life he was living like a monk. The BBC's Max Horberry has been to Barcelona to see Gaudí's work and speak to the people who have been working to finish the Sagrada Familia and campaigning for Gaudí's sainthood. He finds out more about the path to sainthood and how architecture, nature and religion intertwine in Gaudí’s life.