Spoiler alert: This post contains spoilers for the sixth season finale of Game of Thrones.
Each episode of Game of Thrones has started the same way since the show began in 2011: The camera zooms inside an armillary sphere and pans across a three-dimensional map of Westeros and Essos as various structures form and the credits run. Now, according to Hello Giggles, the season six finale has finally revealed the origin of one object from the credits that has been staring us in the face for all 60 episodes.
In the finale, Samwell Tarly arrives at Oldtown to begin his training as a Maester. He's soon brought into the Citadel's library, where he's surrounded by countless books that cover all of history. As we watch Samwell stand awestruck, the camera pans around the library and shows armillary spheres doubling as chandeliers that work with smaller armillaries to reflect sunlight onto the stacks.
A brief close-up of one of the spheres shows that it has symbols that are similar to the ones shown in the credits. According to the Game of Thrones wikia, the spheres have reliefs depicting major historical events, including Robert's Rebellion and the Doom of Valyria, so it would make sense that they would hang in the place where all the world's recorded knowledge is kept. Because the library has just been introduced, the importance of the armillary spheres hasn't yet been explored, but having them in the opening credits is almost certainly not a coincidence.
[h/t Hello Giggles]