In the first Assassin's Creed game, Altaïr's home base is Masyaf.
Masyaf is a mountain fortress in Syria and the headquarters of the Assassin Brotherhood during the game's 12th-century storyline. Altaïr Ibn-La'Ahad returns there after missions to receive guidance, report to Al Mualim, and improve his equipment and abilities.
The game also features three major cities—Jerusalem, Acre, and Damascus—but none is Altaïr's permanent headquarters. Players travel between these cities from Masyaf using the game's world map and fast-travel system. Masyaf itself serves as the setting for the opening and closing portions of the adventure.
Historically, Masyaf is associated with the Nizari Ismaili state and the fortress traditionally linked with Rashid al-Din Sinan, often called the “Old Man of the Mountain.” Assassin's Creed fictionalizes this history and places Altaïr within an imagined Assassin order.