Noun
telesterion
A building used to celebrate sacred rites in Ancient Greece.
Before mystai could enter the Telesterion, they would recite, "I have fasted, I have drunk the kykeon, I have taken from the kiste ("box") and after working it have put it back in the kalathos ("open basket"). Source: Internet
Then on 20th and 21st Boedromion, the initiates entered a great hall called Telesterion ; in the center stood the Anaktoron ("palace"), which only the hierophants could enter, where sacred objects were stored. Source: Internet
Then, Demeter is sitting on the kiste inside the Telesterion, with Persephone holding a torch and introducing the initiates. Source: Internet