How do you one-up a giant luminous glass cube on 5th Ave? With an even larger store in Grand Central Terminal. Apple is set to open its largest store yet, in Manhattan’s historic train station—larger even than the 16,732 square foot shop in London at Covent Garden. It would be a big expansion for Apple, and another step in Grand Central’s transformation from a historic train station to a modern shopping destination. The store will likely open in September.