It’s virtually unknown in the Empire, and kept that way on purpose, but is spoken of in hushed whispers by the Zhaaneph as part of their raving, incoherent prophecies on the mortal reincarnation of their Lord. From what little I knew beyond the name, Deepscorn was just such a prison for those with the Gift, where their abilities were either removed, suppressed, or rendered ineffective, depending on which story I hear. Nozebra knew where it was exactly, because of course nozebra would just happen to know the location of a secret prison. But it was largely agreed upon that it had to reside somewhere deep within the Great Banded Desert. That made sense to me: travelling that enormous, scorching, and ever-shifting hell on Equus required either a death wish, extensive preparation with at least twice one’s body weight in water alone, or being a member of the Zhaaneph’s desert raiders, who apparently had special armour and alchemy to stave off the heat and retain as much water as possible. All in order to attack Imperial settlements near the Desert without any fear of reprisal, as pursuit would be suicide.