I once saw a reference to a specific artificial world and never managed to track down the actual story, wondering if anyone can help id this. The world in question was a flat disk with a sun at the center, sort of like if Saturn's rings were solid and Saturn itself were a star. Every point on the surface would be in a state of perpetual sunrise/sunset. I've no idea if this was a short story, a novel, or what.
Possibly the Discworld series by Pratchett
It could be Pratchett, he has written stories other than those in Discworld; one of them is Strata. It is about a woman who is a world builder. She and some aliens team up to investigate an obviously artificial world. It is a representation of old medieval myths about the world. The world is flat, the sun sits in the centre of the world, stars are points on the globe of heaven.
It turns out to be some sort of easter egg, left by the beings who created the universe.
This sounds like Larry Niven's Ringworld.