From Tar Valon Library
The Dark One has a far greater control over Shayol Ghul and the surrounding region than he does over any other place in the world. Therefore, his followers travel there to commune with him and pledge their oaths to him. According to the Prophecies, Shayol Ghul is the place where the final stages of Tarmon Gai'don will take place. Channeling the One Power at the Pit of Doom is considered to be a great risk.
During the Age of Legends, prior to the drilling of the Bore, the area where Shayol Ghul now exists was a lush island resort (TWoRJTWoT).
The Bore itself does not actually exist in Shayol Ghul. Instead, the Bore exists everywhere, but Shayol Ghul is the place where it can best be detected (This passage needs a reference).