To mark the papal visit to the UK, a camera crew has spent a year filming a world that few have ever seen. With unprecedented access to the Vatican and the people who live and work there, this is a unique profile of the heart of the Catholic Church and the world's smallest sovereign state. Archivists reveal the Vatican's secrets, including the signed testimony of Galileo recorded by the Inquisition. A cardinal journeys deep below St Peter's Basilica to inspect the site claimed to be the tomb of the saint himself, and curators share a private viewing of Michelangelo's extraordinary decoration of the Sistine Chapel. An intriguing behind-the-scenes look at the workings of one of the world's most powerful and mysterious institutions.

• National Geographic