At the heart of the episcopal group founded in the 4th century, the present cathedral (13th century) contains unsuspected treasures: the monumental ciborium, the tomb of the bishops, the chapel where Saint Hugues welcomed Saint Bruno, the frescoes of Father Guétal… Many famous people are linked to its history: the dolphins of Viennese, the knight Bayard, Catherine de Medicis, Molière, Stendhal, Napoleon III… The visit allows us to discover one of its little-known ornaments, usually closed to the public: the cloister of the canons, still provided with its Romanesque capitals, and in which remains of some of the oldest wall paintings of the Isère have been exposed.