The Gazing-Pool, located in the Augury, was the interface between the sentient heart of Crivello's Cauldron and the human inhabitants of the Cauldron's system. It served as aa "window onto worlds as yet unseen", allowing "communications seer" Ptolemy Muttonchops to see visions of the future. Unbeknownst to Ptolemy, the reason only he could use the Gazing-Pool was that he was not a human, but an avatar of the Cauldron, generated by it just like the Gazing-Pool itself.
Ptolemy checked the Gazing-Pool every morning at "ten minutes past the hour of the nadir". It was usually "clear, immutable, certain". One morning, on the other hand, it appeared clouded and hazy before resolving into an apocalyptic vision of a Black Sun Rising, from which demons streamed out to bring about "Abaddon… the end of all things". This vision was later realised as the Dalek Hive manipulating the Cauldron's link to the Eighth Doctor to turn it into a black hole singularity that permitted travel to and from the rest of the Omniverse, causing Great Vampires and alternative Daleks to pour out and all possible universes to begin colliding into a single hellish reality. However, the process was halted by Muttonchops, who sacrificed his individual existence to cause the singularity to collapse. (COMIC: Fire and Brimstone)