In Season 2 of Game of Thrones, Daenerys Targaryen's dragons are stolen by the Qarthian warlock Pyat Pree. To get them back, she must venture into the warlocks' lair, known as the House of the Undying. But she gets a lot more than she bargained for within its walls. She's treated to a revealing but enigmatic vision of the future. Now that several seasons have passed, fans are starting to believe that Daenerys' vision in the House of the Undying could answer a lot of Game of Thrones questions. And that information is especially important to have now that the end is fast approaching.
But what happens in Daenerys' vision? Season 2 was a long time ago, so you're forgiven for forgetting. In it, Daenerys finds herself in the throne room at King's Landing, though it's dark and empty and the roof has caved in. The ground is covered in snow, and more falls gently on the Iron Throne through the ragged openings in the ceiling. Before she can touch the throne, Daenerys hears her dragons calling; she follows the noise outside into a blizzard so thick and white that barely anything is visible at all.
But there is a Dothraki tent there and inside it is Khal Drogo with their infant son. Dany tells him that this vision is "dark magic," but then amends that perhaps she's dead after all. Drogo argues that he just refused to move on to the next world without her. He speculates that the whole thing could be a dream before the sound of dragons once again draws Dany away. That's how it ends.
Some viewers believe this vision foreshadowed Dany's eventual fate, but theories vary. Reddit user Fooking Kneelers thought it foretold a choice Dany would have to make one day. She could either take the throne and become queen or save her family. In the vision, Dany never laid a hand on the throne, so it seemed to indicate that she would put her dreams of ruling aside for the sake of her loved ones. They believed Daenerys would have a baby with Jon, but she would never sit on the Iron Throne.
Redditor marisaann26 had a slightly different idea about the vision. They thought the Night King wanted Dany to be his new queen, or to take over his role and become the Night Queen. He would cause the deaths of her remaining dragons, which would lead Dany to join his army so that she could be reunited with them. She would follow her dragons' cries like in the vision and end up on her own ice throne. It's a more metaphorical analysis, but not necessarily impossible.
User Mother of Dragons presented another possibility: Dany leaving the throne to go after the dragons symbolized her helping Jon (a Targaryen) instead of being queen. The snow on the throne implied that either Jon would become king, or the Night King would truly take over Westeros.
While the theories about Dany's vision in the House of the Undying all explore various possibilities, they seem to agree on one thing: Daenerys will not be queen of the Seven Kingdoms. Everything else is up for debate. Will she give up her goals for her dragons, or perhaps reunite with Khal Drogo in the afterlife? Does the snow on the throne mean the age of Aegon Targaryen is about to begin?
Any of those options is plausible because the vision leaves so much open to interpretation. But it looks like Dany will have a choice to make sometime in the next four episodes. What that choice is remains to be seen.