The Ziggurat was a magical research facility in Estorium. It was magically constructed to have more interior than exterior space to allow magical experiments to be conducted far away from each other while still in the same structure.
In the year 2145, the Tear of Boccob was sent to the wizards at the Ziggurat for research and experimentation. One of them, a wizard named Kask, used it to transform the red dragon Rukaleth into a dracolich. When the other wizards reacted with horror, Kask and his followers used the Tear to slay them. The other wizards, however, had used the artifact to create an hourglass capable of altering the flow of time itself, and used it to defeat Kask and his followers, sealing their bodies in the Ziggurat's lower chambers.
Like the rest of Estorium, the Ziggurat was abandoned following the Illithid War. It was taken over be a race of insectoid aberrations called sebaceans after Tephra opened a portal to the Far Realm in 2959; the creatures freed Kask - now an undead mass of worms and maggots - and began seeking the hourglass. Ultimately, the Challengers of the Unspeakable slew all of the sebaceans and Rukaleth, claimed the hourglass for themselves, and defeated Kask. Though the larva mage would eventually reconstitute his form, it is unknown if he returned to the Ziggurat.
It is rumored that Estorium's new queen, Vyrellis, has restarted the Ziggurat's magical research programs in the wake of the empire's rebirth.