Catching the train from London to Istanbul means a first stop in Paris, it was the same in 1889 on the original Orient Express, except in those days there was a ferry involved; and you had to dress smartly for dinner, run the risk of being murdered etc. And Istanbul was called Constantinople – there’s a song about that, written in 1953.
Although this photo booth in Montmartre is something of a Paris icon, passports aren’t needed after leaving London, given the warm embrace of the Schengen Zone, until three hours inside Turkey at three o’clock in the morning – but that’s another story.