Pit of Doom
The Pit of Doom is the place in Shayol Ghul in which the Dark One can be sensed and communicated with. It is reached through an opening in the mountain, the only one from which no smoke is emitted and leads to a lake of molten rock, underneath cloud swept sky, that is not the one outside the mountain (LoC, Prologue). The Forsaken swore to the Dark One in the Pit of Doom (TFoH, Ch. 18. Other servants of the Dark One are occasionally taken there to relay information or receive orders, but this is very rare (TFoH, Ch. 19). It is often used to refer to any unpleasant experience (TGH, Ch. 23; TFoH, Ch. 29; WH, Prologue). The last battle is prophesied to take place in the Pit of Doom (TGH, Ch. 26).
It is dangerous to channel at the Pit of Doom unless expressly given permission (LoC, Prologue; ACoS, Ch. 25). This is a matter of the Dark One consciously acting, though interactions between the One Power and him, the source of the True Power, can be unpredictable. Anyone channeling in the Pit of Doom without permission can expect swift punishment on the assumption that failure to ask permission means you intend to do something he won't like. It isn't that he believes anyone can harm him, just that he is in charge, and your failure to ask permission, your presumed intention to do something he wouldn't like, means that your faithfulness quotient has just suffered a severe downturn (Robert Jordan Question of the Week, Week 9).
In these southlands, spring felt like summer, and summer like the Pit of Doom (The Fires of Heaven, Chapter 29).
"He is going to lead our armies to victory. And make my life the Pit of Doom" (Siuan about Gareth Bryne, The Fires of Heaven, Chapter 29).
“a lake of molten stone, red mottled with black, where man-high flames danced, died and rose again .There was no roof, only a great hole rising through the mountain to a sky that was not the sky of Thakan'dar. It made that of Thakan'dar look normal, with its wildly striated clouds streaking by as though driven by the greatest winds the world had ever seen. This, men called the Pit of Doom, and few knew how well they had named it.” (Lord of Chaos, Prologue).
"Who in the Pit of Doom lives there?" (Mat, A Crown of Swords, Chapter 14).
"To the Pit of Doom with custom if need be" (Cadsuane, A Crown of Swords, Chapter 19).