Sit in Grace Cathedral in San Francisco on a weekday evening and you may witness a silent army laying siege to the altar. They arrive alone or in pairs with mats rolled under their arms and it is only when the instructor arrives that you realise that a yoga class is about to begin.

Only in San Francisco? Perhaps, but the idea of using a sacred space for yoga seems a stroke of genius, even in this most liberal of churches. In a nearby chapel, there is a triptych by the artist Keith Haring, completed just weeks before he died of Aids, along with symbols of the world’s religions from Jainism to Islam.