Temple of the Mind's Eye
From Syra D&D Wiki
The Temple of the Mind's Eye is a temple in the Estorian city of Derenath. Before Estorium's fall, it was perhaps the greatest temple to Boccob ever built.
In the year 2959, the Challengers of the Unspeakable were sent inside the temple's ruins to stop a mind flayer from opening a portal to the Far Realm. Inside they discovered the mind flayer using the Scythe of Nerull to open his portal, and though they killed it the wizard Tephra completed his work and opened the portal herself.