There has been a collection of religious objects and relics in the cathedral since the 11th century which were put on permanent public display in 1892 and moved to the current museum in 1956. The absolute highlight is a hexagonal emerald bowl; the Holy Basin (Sacro Catino), thought by some to have been used during Jesus’ Last Supper. A 13th century Byzantine gilded silver cross bears fragments of the True Cross and a plate from the Roman imperial era is said to have been the one John the Baptist’s severed head was placed on (make sure you ask to see the magical transformation of plate when it’s illuminated). There’s also a silver casket holding the ashes of the saint too! The small museum itself is an atmospheric underground journey with dramatic spotlights and grey stone, the perfect setting for a treasure museum.