St John's Co-Cathedral, Malta's most impressive church, was designed by the architect Gerolamo Cassar. It was built between 1573 and 1578, taking over from the Church of St Lawrence in Vittoriosa as the place where the Knights would gather for communal worship. The interior was revamped in the 17th century in exuberant Maltese baroque style, and it's an astounding surprise after the plain facade. One of its greatest treasures is a huge painting of John the Baptist by Caravaggio.
The nave is long and low and every wall, pillar and rib is encrusted with rich ornamentation, giving the effect of a dusty gold brocade. The floor is an iridescent patchwork quilt of marble tomb slabs, and the vault dances with paintings by Mattia Preti that illustrate events from the life of St John the Baptist.
Beyond here, the Oratory contains two paintings by Caravagggio, and the Cathedral Museum houses the beautiful 16th-century Graduals of L-Isle Adam, illuminated choral books and a magnificent collection of 17th-century Flemish tapestries based on drawings by Rubens.
It was raised to a status equal to that of St Paul's Cathedral in Mdina – the official seat of the Archbishop of Malta – by a papal decree of 1816, hence the term 'co-cathedral'.
Visitors should dress appropriately for a house of worship. Stiletto heels are not permitted, to protect the marble floor.