Attack on Titan season 3 episode 19 The Basement
Armin has a nightmare of a weeping Colossal Titan, waking up with no memory of the events following Bertholdt's transformation. The eight remaining members of the Survey Corps huddle around him to explain their situation, Armin struggling with Levi's decision to bring him back instead of Erwin. Hange, Levi, Eren and Mikasa proceed into Shiganshina to investigate the basement of what remained of Erenâ€™s home. Levi kicks open the basement door when Grisha's key cannot unlock it, the group learning that it actually opens a desk drawer with a hidden compartment containing three well-preserved books. The group find one books holding a strange picture of Grisha, standing next to a woman holding an infant child who are neither Karla or Eren. An inscription written by Grisha on the back explains the picture to be a photograph created by technology from a land beyond the walls, where people live in luxury. As what remained of the Survey Corps return to the city, Nile Dok confines to the council that Erwin once considered the possibility that may be humans living beyond the walls.
In a post-credits scene Eren begins reading Grisha's book, which opens with Grisha recounting a time in his youth when he and his sister, Fay, lived in a city beyond Mitras and Wall Maria, the world Eren knows today. The children watched an airship fly overhead, and against their mother's instructions, Grisha impulsively dragged Fay beyond the walls of their district to watch it land.