I've never taken this twinning business seriously: but I can think of a twinning which ought to be (but isn't) signed and sealed: Avignon and Exeter, the Anglican diocese where I served before we returned to Oxford.
The Avignon Papacy has had a bad press; Petrarch was only one of those who left behind him highly tendentious writings which have fastened upon the period when the Sovereign Pontiffs lived in Avignon a reputation for corruption and venality. But when Pam and I were there (while we were still Anglicans), it completely stole our hearts. I developed a soft spot especially for John XXII. It was he who in fact (forget Urban IV and Transiturus) launched upon the Western Church the cultus of the Blessed Sacrament: Exposition, Processions and all. He ordered the observance of Trinity Sunday; the bowing of the head at the Holy Names of Jesus and Mary; the ringing of what came to be regarded as the evening Angelus; the use of the prayer Anima Christi (of which he has been suspected of being the author). He promoted literati and encouraged the study of Greek and Latin grammar. He fostered the veneration of our Lady; the statue which he gave of our Lady 'All-powerful' still exists in the Cathedral at Avignon - of which he was bishop before he became Pope. You might well conclude, as I did, that he was one of the grandfathers of the Counter-Reformation.
But what's the Exeter connection? He 'provided' one of his close proteges and friends to be Bishop of Exeter -- John de Grandisson (pronounced 'Grahns'n'), a member of a noble and cosmopolitan Burgundian family, who thus became one of the great builders of Exeter Cathedral and a patron of the arts so powerful that in a 1988 London exhibition he still merited, despite the depredations of Time and of the Tudors, an entire section of his own. He possessed a Hebrew grammar; he codified and reformed the usages of his Cathedral Church; manifested a fierce and protective devotion to the Mater Misericordiae and attempted to lure his Cathedral clergy to bow their heads at the mention of her name. He bequeathed to his Cathedral and to his foundation at Ottery monstrances which must count as two of the most splendid pieces of medieval metalwork of which we have detailed records.
And there is a mystery about John XXII of which I can't help feeling that Grandisson just might be the key. The pope's tomb, in Avignon Cathedral, is a superb piece of ... yes, English workmanship.
If you find yourself there, you could do worse than to worship on Sunday morning in the Chapel of the Black Penitents: an exquisitely baroque masterpiece which is served by the Society of S Pius X. Although I made my Anglican clerical status very clear to them, they were extremely welcoming. In fact, a much friendlier lot than those at the 'mainstream' church which we had visited the evening before for a Vigil Mass. The Chapel of the Black Penitents, unlike so many French churches, had a predominantly young congregation and we weren't 'conducted' by a officious layperson or regaled with guitars.