Alamut Temple

The Alamut Temple was a small First Civilization temple located beneath the Assassins' fortress in Alamut. It was used to store dozens of Memory Seals.

Sometime between 1228 and 1247, during his exile in Alamut, Altaïr Ibn-La'Ahad discovered the temple and claimed six of its Memory Seals, of which he later used five as the Masyaf Keys necessary to open the door to his library beneath the fortress in Masyaf.

Reference

 * Assassin's Creed: Revelations Official Game Guide