Atlantis

"Atlantis was a great city with palaces and temples and learned men" says Uncle Andrew to Digory when Polly vanishes out of our world into the Wood Between the Worlds. The Atlantean Box which his 'fairy'god mother;Mrs. Lefay, had given him contained something that had been brought from another world just when our world was only just beginning. She had made him promise not to open the box and to burn it as soon as she died; but Mr. Ketterly broke this promise.