Strata by Terry Pratchett

In a universe where planets are manufactured by a mysterious company, a skilled planet builder named Kin Arad embarks on a journey to explore a peculiar flat world. Accompanied by an eclectic crew, including a four-armed alien and a time-traveling Neanderthal, Kin uncovers secrets that challenge her understanding of reality and the nature of creation. As they navigate this bizarre world, they encounter strange creatures and face existential questions, ultimately leading to revelations about the universe's origins and the true purpose of their mission.