Masyaf serves as the Assassins' headquarters in the original Assassin's Creed.
In the game, Masyaf is a fortified mountain settlement in Syria and the home of the Assassin Brotherhood led by Al Mualim. Altaïr Ibn-La'Ahad returns there between missions to receive instructions, report progress, and advance through the story.
Masyaf is not one of the major target cities that Altaïr visits during the main investigation. Those cities include Jerusalem, Acre, and Damascus, which is why players sometimes mix the headquarters up with a mission location. Masyaf instead functions as the Brotherhood's central base.
The settlement is based on the real Syrian town of Masyaf, which has a prominent medieval castle. The historical site is associated with the Nizari Ismaili community and later became an important reference point in popular accounts of the medieval Assassins.