The Sanctuary is the secret library beneath Villa Auditore at Monteriggioni in Assassin's Creed II.
Ezio discovers the hidden chamber below the Auditore family villa after returning to Monteriggioni. The room contains statues representing legendary Assassins and serves as a private record of the Brotherhood's history. It is one of the villa's most important secrets rather than a normal public library.
The Sanctuary is connected to the game's wider search for Altaïr's armor. Six seals are needed to unlock the armor displayed in the chamber. Each seal is associated with the tomb of a notable Assassin, leading Ezio to hidden locations across Italy.
The room is sometimes confused with the Vault, a separate ancient site tied to the Pieces of Eden and the First Civilization. The Grand Temple is also a different location introduced in later storylines. Monteriggioni itself functions as Ezio's economic and operational base, while the Sanctuary provides a historical link between generations of Assassins.