The CERN scenes were shot at the real-life CERN headquarters on the Swiss/French border - home to the Large Hadron Collider.
Much of the movie centers around the worlds smallest independant state, Vatican City, and the famous St Peter's Sqaure and Basilica. However the film makers were forbidden from officially filming here by the Catholic Church, thought there are aerial shots and director Ron Howard confessed that they had secretly shot some footage for the film at this location.
UCLA's Royce Hall stands in for St Peter's with the help of some props and fake stained glass windows.
Having been denied access to the real Valican by the church the film makers uses the Caserta Palace near Naples as one of their stand-ins - it had previously been used as a substitute for the Vatican in Mission Impossible III.
Having no access to fim in the real Vatican Library, these scenes where filmed here at the Biblioteca Angelica near Piazza Navona.
The 'Little Europe' street set on the Universal backlot stands in for the streets of Europe
Piazza del Popolo exteriors were used for the 'Earth' murder scenes around Santa Maria del Popolo. The church was not accessible to the film makers having been banned from using the location by the Catholic Church.