Great Old Ones' universe

By some accounts, the Great Old Ones originated from the previous universe which had existed before N-Space, (PROSE: Millennial Rites, Synthespians™, Divided Loyalties) the "Space before this" which The Book of the Old Time described as having "Being before this" in the "Time before this". (PROSE: Christmas on a Rational Planet, The Quantum Archangel) This reality had different physical laws, more based in magic, which gave its survivors great power in other realities. (PROSE: Millennial Rites, Synthespians™, Divided Loyalties)

Disputed nature
Some accounts indicate that the "Space before this" was actually N-Space in the pre-chronological time before the Time Lords imposed Rational history, (PROSE: Christmas on a Rational Planet, The Parliament of Rats) also known as the Dvapara Yuga, (PROSE: Dharmayuddha) Dark Time, Old Time, or Time of Chaos. (PROSE: Cat's Cradle: Time's Crucible, Christmas on a Rational Planet, et al.) This perspective viewed the 'previous universe' hypothesis as a misunderstanding of the truth arising from small-mindedness. (PROSE: Christmas on a Rational Planet)

A similar account indicated that the universe from which the elder races originated was actually the original palimpsest universe. (PROSE: Mr Saldaamir)

Several accounts indicated that the Elder Gods originated in the Old Time, shortly after the Big Bang. (AUDIO: The Magic Mousetrap) Within this context, the Seventh Doctor nonetheless claimed that the Elder Gods originated from "the old universe". (AUDIO: Signs and Wonders)

Creation
According to The Record of Rassilon, this universe most likely had prior ancestor-universes before it, including that of the Gods of Ragnarok, who had destroyed the universes before this one. These Gods survived into the newborn universe as powerful beings. (PROSE: Divided Loyalties) The Seventh Doctor believed that this universe existed as part of the cyclical nature of the universe, which periodically went through cycles of expansion and contraction punctuated by Big Bangs. (PROSE: All-Consuming Fire)

Existence
A set of physics developed which was based on quantum mnemonics. The heavens were green and the stars looked like giant doughnuts. Time was "strange".

An equivalent of the Time Lords emerged, and came to rule this universe via magic. (PROSE: Millennial Rites) They were far more advanced and evolved than the Time Lords of the Doctor's universe. (PROSE: Divided Loyalties) Yog-Sothoth was their military strategist. (PROSE: Millennial Rites)

Destruction
By one account, this universe was destroyed by the Gods of Ragnarok. (PROSE: Divided Loyalties) As the universe reached a point of collapse, a group of its Time Lords briefly shunted themselves sideways into a parallel universe which ended a split-second later, thereby allowing themselves to survive the Big Bang and return to the newly-created N-Space. (PROSE: Millennial Rites, All-Consuming Fire)

According to the Sixth Doctor, the Toymaker originated in another universe before the Doctor's and was hauled into the Doctor's universe by some kind of catastrophe. (AUDIO: The Nightmare Fair)

This universe and its replacement were forever separated by a point where time and space didn't exist, forever separating the two. (PROSE: All-Consuming Fire)

Legacy
The survivors of this universe became the Great Old Ones, powerful because the usual laws of physics didn't apply to them. According to The Toymaker, they initially used their powers for other things in the beginnings of the universe, but some eventually got bored of thousands of millennia of pointless creation and pointless destruction and turned to other things. (AUDIO: The Nightmare Fair)

The Time Lords had records of "the universe before theirs" in the Matrix, which the Sixth Doctor accessed in the Matrix during his time as Lord President. He later described it to Anne Travers. (PROSE: Millennial Rites)

The Warrior knew that the Old Ones in the Wilderness Beyond Time came from the universe before his own. (AUDIO: The Key To Key To Time)