No airline has ever offered direct flights on the route from AAL to ZYR. Those three-letter International Air Transport Association (IATA) codes used on airline baggage tags can be enigmatic, evocative or just puzzling. Some are easy to decode. It’s no surprise that AAL is the Danish town of Aalborg, where this summer’s destination list includes AMS, OSL and STN — all easily guessed as the code derives directly from the city or airport name, viz. Amsterdam, Oslo and Stansted. Some airline codes make perfect matches. LTQ could only ever be Le Touquet, just as nothing could fit Nice more nicely than NCE.

But what of the airport code ZYR? Well, that’s not an airport at all; it is a railway station in Belgium. The Dutch airline KLM will gladly book you a ticket from ZYR to Berlin or Bujumbura — or, indeed, to dozens of other cities across the world, provided you don’t mind taking a train for the first part of your journey. The code ZYR is assigned to Brussels Midi station, from where passengers booked though KLM can travel on a direct Thalys train to Schiphol Airport near Amsterdam to join their flight.

So some IATA airport codes refer to places far from any airport. QYG ranks as one of the quirkiest ‘non-airport’ codes.