Rip Van Winkle
Nor will it be forgotten how one of the Sultans one day expressing doubts on the possibility of so much having happened to the Apostle in so short a time, a learned doctor of the Mohammedan law caused a basin of water to be brought and requested him to dip his head into it. When the Sultan dipped his head he found himself in a strange country, alone and friendless, on the seashore. He made his way to a neighbouring town, obtained employment, became rich, married, lived seven years with his wife, who afterwards, to his great grief, died, and then he lost all. One day he was wandering in despondency along the seashore, where he had first found himself; and in his despair he determined to cast himself into the sea. Scarcely had he done so when he beheld his courtiers standing around his throne: he was once more Sultan, and the basin of water into which he had dipped his head was before him. He began furiously to reproach the learned doctor for banishing him from his capital and sending him into the midst of vicissitudes and adventures for so many years. Nor was it without difficulty that he was brought to believe that he had only just dipped his head into the water and lifted it out again.
— Edwin Sidney Hartland, ‘The Science of Fairy Tales: An Inquiry into Fairy Mythology’
World of Warcraft.
A Danish tradition, however, runs that a bride, during the dancing and festivities of her wedding-day, left the room and thoughtlessly walked towards a mound where the elves were also making merry. The hillock was standing, as is usual on such occasions, on red pillars; and as she drew near, one of the company offered her a cup of wine. She drank, and then suffered herself to join in a dance. When the dance was over she hastened home. But alas! house, farm, everything was changed. The noise and mirth of the wedding was stilled. No one knew her; but at length, on hearing her lamentation, an old woman exclaimed: “Was it you, then, who disappeared at my grandfather's brother's wedding, a hundred years ago?”
In Rocannon's World by Ursula K. Le Guin, a woman travels by spaceship to a far-off world to retrieve a family heirloom from a museum, not realising that relativistic effects of near-light-speed travel will cause time to pass far more slowly for her than for her home planet. She returns – after what she experiences as only a matter of days – to find her daughter grown up and her husband dead.
Relativistic time-dilation is real, although we have not yet applied it at any significant scale.
We now have the power to make two particular categories of fairytale entirely real. I'm not sure what this means.