DISCWORLD IS REAL. It's the way worlds should work. Admittedly, it is flat and goes through space on the backs of four elephants which stand on the shell of a giant turtle, but consider the alternatives. Consider, for example, a globular world, a mere crust upon an inferno of molten rock and iron. An accidental world, made of the wreckage of old stars, the home of life which, nevertheless, in a most unhomely fashion, is regularly scythed from its surface by ice, gas, inundation or falling rocks travelling at 20,000 miles an hour.

Such an improbable world, and the entire cosmos that surrounds it, was in fact accidentally created by the wizards of Unseen University.[1] It was the Dean of Unseen University who in fact destabilised the raw firmament by fiddling with it, possibly leading to the belief, if folk memory extends to sub-sub-sub-sub-atomic particle level, that it was indeed all done by somebody with a beard.

Infinite in size on the inside, but about a foot across on the outside, the universe of Roundworld is now kept in a glass globe in UU, where it has been the source of much interest and concern.
Mostly, it's the source of concern. Alarmingly, it contains no narrativium.
Narrativium is not an element in the accepted sense. It is an

[1] The greatest school of magic on the Discworld. But surely you know this?

attribute of every other element, thus turning them into, in an occult sense, molecules. Iron contains not just iron, but also the story of iron, the history of iron, the part of iron that ensures that it will continue to be iron and has an iron-like job to do and is not, for example, cheese. Without narrativium, the cosmos has no story, no purpose, no destination.

Nevertheless, under the ancient magical rule of As Above, So Below, the crippled universe of Roundworld strives at some level to create its own narrativium. Iron seeks out other iron. Things spin. In the absence of any gods to do the creating of life, life has managed, against the odds, to create itself. Yet the humans who have evolved on the planet believe in their hearts that there are such things as gods, magic, cosmic purpose and million-to-one chances that crop up nine times out of ten. They seek stories in the world which the world, regrettably, is not equipped to tell.

The wizards, feeling somewhat guilty about this, have intervened several times in the history of Roundworld when it seemed to them to be on the wrong track. They encouraged fish (or fish-like creatures) to leave the seas, they visited the proto-civilisations of dinosaur-descendants and crabs, they despaired at the way ice and falling comets wiped out higher life forms so often - and they found some monkeys who were obsessed with sex and were quick learners, especially if sex was involved or could, by considerable ingenuity, be made to be involved.
Again the wizards intervened, teaching them t...