St John's Co-Cathedral

From the street, St John's Co-Cathedral gives little away. Girolamo Cassar designed it for the Knights of St John in the 1570s, and its limestone front is plain, almost severe. Inside it is another building entirely: in the 1660s the Calabrian painter Mattia Preti covered the vaulted ceiling with scenes from the life of St John, and nearly every surface below is carved, gilded or painted.

Look down as well as up. The floor is a patchwork of inlaid marble tombstones, each marking a knight or officer of the Order, with coats of arms, skulls and inscriptions picked out in coloured stone. The side chapels belonged to the Order's langues, its national groups of knights, and each tried to outdo the others.

The painting most people come for hangs in the oratory. Caravaggio painted The Beheading of Saint John the Baptist here in 1608, during his short time as a member of the Order. It is his largest work and the only one he signed, in the blood spilling from the saint's neck. It was one of the two places we made a point of seeing again when we came back to Valletta on a cruise.