Undiscovered by the Malledhrim until just before the fortress's destruction, these darkened halls are where Sauron recovered in secret following his defeat in the War of the Last Alliance. Shadowy impressions from his presence remain, revealing themselves to those who dare explore his hidden throne.
Access is from a secret stair before the fortress is cast down, and a trapdoor afterwards, during the quest Whispers in the Pits.
-  Chapter 5.3: Whispers from the Long Years
-  Whispers in the Pits
The Room of Voices, where Sauron recovered and held audiences in secret.
Sigileth's hideout in the Sorceror's Stores.