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On the edge of Piazza Navona, one of the grandest squares in central Rome, Barry and Linda, visitors from Texas in the US, stepped out of a golf cart. They planned to cross the square on foot, perhaps stopping to admire Lorenzo Bernini’s 17th-century Fountain of the Four Rivers, before being picked up by their driver at the opposite end.

The couple had already done a walking tour on day one of their trip, and had been so exasperated by a stifling three-hour shuffle along a corridor towards the Sistine Chapel on day two that by the third day they wanted to give their tired feet a rest.