Some time ago, Prince Hassan of Jordan, so I believe, suggested that Cordoba Cathedral should be swapped for Hagia Sophia ... each building thus returning to the religion, Moslem or Christian, which originally built it. But I am glad that idea came to nothing. Celebrating the Eucharist in a former mosque can be a joyous experience; I remember, in Crete, many years ago, going to the Divine Liturgy in the Church of S Titus, which still retained all the glorious architectural features of the mosque it had once been (built, needless to say, on the site of a church ... such is the Levant).
Rambling still further: I recall a superb Orthodox church on the waterfront at Rhodes, which was built by the Italians and, after the war, "purified from the dogma of the Latins" and adorned with very fine murals in mid-Byzantine style. Rather more depressing is the Hospital Chapel in Exeter; the area directly in front of the Aumbry, where the Blessed Sacrament was reserved, is set aside for Moslem prayer and equipped with prayer-mats.
My local Greek Cypriot church along the Camberwell New Road in South London had started life as a "Catholic Apostolic" (Irvingite) church; and the Ukrainian Greek-Catholic Cathedral in Mayfair was originally the King's Weigh Chapel, a very high church Congregationalist place of worship (I believe the minister, a Dr Orchard, had secured 'vagans' ordination; he eventually ended up as a Catholic priest). Didn't the SSPX church in London begin as a church for Welsh Anglicans? I wonder if they honour their origins by singing Cwm Rhondda at Benediction (not a stupid idea ... you just think about it).
Heading off at a slight tangent ... do British readers recall that marvellously surreal occasion when somebody had himself filmed ranting against Islamic infiltration with Westminster Cathedral immediately behind him ... poor, dim, soul, he had thought it was mosque.
Ah, the thought of the Call to Prayer (Extraordinary Form, I would hope) resounding in Latin from that lofty minaret!
(One of the ... er ... many oddities about Oxford is the very attractive empty mosque built on the Magdalen College vegetable patch but, I believe because of financial complications, never opened. It would make an unusually fine Quaker Meeting House. Magdalen, come to think of it, could be converted into a pretty decent madrassa.)