The Pit of Doom, also spelled Pit of Dhoom, is the area where the Bore in the Dark One's prison is most easy to detect, as well as being the area where he has most control. This area lies under a mountain in the heart of Shayol Ghul. It is a vast and deep lava-filled cavern with a small ledge above it that leads into the tunnels through the mountain, and the top of it is open to the sky. However, the sky above the Pit is not the same as the sky over Shayol Ghul; clouds of various colors and striations pass overhead at speeds far beyond what any terrestrial wind could produce. Despite the Pit's metaphysical proximity to the Bore, in reality the Pit is no physically closer to the Bore than anywhere else in the world. It is also apparently not the physical location of the Bore's first drilling; Shayol Ghul was a tropical tourist destination during the Age of Legends, whereas the Bore was drilled at the Sharom research station at Collam Daane university.
The Pit is the only place where most people can communicate with the Dark One. Doing so makes one feel pain and ecstasy beyond imagining; it is somewhat like the feeling of the True Power. The Dark One has no physical manifestation that he uses, he simply speaks directly inside the mind of whomever he is contacting with an overwhelmingly powerful telepathic "voice". However, it appears not to be strictly the only place where one can communicate with the Dark One, as Moridin could apparently hear direct commands from the Dark One anywhere in the world. However, he was a unique case due to his gross overuse of the True Power.
Reality is twisted and malleable within the Pit of Doom, most likely due to the Dark One's direct influence. Possibly due to this twisting of reality, a mindtrap can be established here and nowhere else in the world. It is revealed that Rand al'Thor can at least reverse the Dark One's reality tampering here, though the mechanism behind this can only be speculated to be related to his ta'veren nature, unique among even ta'veren individuals as he was also the Dragon Reborn.
Channeling in the Pit of Doom can be sensed by the Dark One. Channeling in the Pit without permission is a sure way to anger him, and death is invariably swift. Additionally, anyone except Moridin who might attempt to channel the True Power in the Pit would evidently burn themselves to a cinder due to the Dark One's metaphysical closeness to the Pit. Why Moridin seems to be able to channel the True Power there is a mystery.
During the Last Battle, the Dark One "hatched" a tiny portion of his being from Shaidar Haran in the Pit, which resulted in an absolutely empty patch of nothingness coming to exist there. This void emptied the Pit of it's lava and quenched all of it's fires, leaving little more than a pitch black hollow beneath Shayol Ghul.