In Assassin’s Creed Revelations, the device used to access Altaïr’s memories is the set of Masyaf Keys.
The Masyaf Keys are ancient artifacts that Ezio Auditore seeks in Constantinople. They unlock the hidden library beneath Masyaf, the former headquarters of the Levantine Assassins. Ezio learns that the keys contain memories of Altaïr Ibn-La’Ahad, allowing the game to show important episodes from Altaïr’s later life.
The keys are central to the structure of Revelations. Ezio follows clues across Constantinople and nearby territories while confronting Templar forces and investigating the legacy of the older Assassin. The memories provide a direct narrative link between Ezio and Altaïr, two protagonists from different historical periods.
The Animus is the modern device used by Desmond and other characters to experience genetic memories, so it is not the answer here. The Apple of Eden is a different Piece of Eden, while “Pieces of Eden” is a broad category rather than this specific artifact.