Valletta has an astonishing number of churches for such a tiny population but St John's Co-Cathedral is an absolute must see - despite being swamped by tourists in summer. The Proscenium arches, marble-inlay tombstones, and manically ornamented everything are an incredible testament to the Knights of St John's endless attempts to keep up with the Medicis. And in the back room, a giant Caravaggio. The mercurial Italian spent 14 months on the island painting before duffing up a local organ-player and legging it, leaving in his wake the masterpiece, The Beheading of St John.