The Cathedral Museum occupies the former Seminary building just beside the cathedral, and its collections are considerably more varied than the name suggests. The religious art holdings include works by Mattia Preti, Albrecht Dürer engravings, and a significant collection of Italian Baroque music — manuscripts and printed scores that constitute the most important such collection south of Naples.
The ecclesiastical treasures section displays silverware, vestments, and reliquaries from across the Maltese islands. One room is dedicated to Roman antiquities unearthed during the cathedral's construction, including mosaic fragments and carved stonework. The museum is well-maintained and not crowded even when the streets outside are busy with tour groups.
Admission includes access to the treasury, the coin collection, and rotating temporary exhibitions. Allow about an hour for a thorough visit.