[The content of this article has been produced by our advertising partner.] When Hong Kong architect David Leung flew to Barcelona last autumn for a conference, he did something unusual: he broke the journey in Istanbul for 36 hours. He had a hotel room waiting — complimentary, arranged through his carrier’s stopover programme — and used the time to visit Hagia Sophia, eat a slow lunch of meze overlooking the Bosphorus, and walk through the courtyards of Topkapı Palace. By the time he boarded...