The World and Thorinn is a fix-up novel made from three stories that Damon Knight had published in Galaxy magazine. Thorinn is a young boy who lives with his adoptive family of trolls in Hovenskar, a curious land where the horizon curves upwards. Thorinn is named after a sort of flea, as one of his legs is lame, so he travels via a hopping gait. When earthquakes cause the well to go dry, Thorinn's father sends him in to investigate (and as a sacrifice to the gods) with a geas to "go down." As Thorinn follows the geas, he travels through many lands, surviving by his wits, until he finally reaches the final depth and learns a terrible secret about who he is and what his world is.
This novel exhibits the following tropes:
- Benevolent A.I.: At the core of the Earth, Thorinn encounters "The Monitor", an A.I. that was told to keep humanity safe until given orders to do otherwise. It has been thousands and thousands of years since that command was given, and the A.I.'s idea of keeping humanity safe is to keep them ignorant of the true nature of their world so as to keep them from dangers.
- City in a Bottle: Each of the worlds Thorinn visits is essentially this, with the residents believing that their section is the only one that exists.
- Gravity Screw: As Thorinn goes deeper, the physics of the worlds gets stranger, with part of the justification being that, as he gets closer to the center of the world, gravity becomes more evenly distributed in every direction so that the worlds start heading towards low gravity, then no gravity at the center.
- Hollow World: As Thorinn descends, he finds more and more worlds at every layer, with solid skies. It's ambiguous as to whether Hovenskar, from which he started, is at the surface, covered only by the outermost protective layer, or if it's still some levels deep.
- I Fell for Hours: At one point, Thorinn is knocked into a very deep shaft. He falls for a long enough time for him to drink, to relieve himself, and to attempt sleep. In actuality, he is falling toward the center of the Earth. That it takes longer than it ought to might be a matter of artistic physics or an indication that gravity doesn't work the way we expect.
- Last of His Kind: Throughout his journeys, Thorinn never encounters anyone of the same race as himself. Near the end of the book, he discovers that there are other humans, but that he is still special in being the descendant of the ruling class of humans and thus in the chain of command for the robots.
- Liberty Over Prosperity: Thorinn is faced with this choice near the end of the book. If he gave the word, The Monitor would turn over all operations to him. But he knows that it would do a better job than him. And yet, it has also essentially enslaved humanity...
- Maybe Magic, Maybe Mundane: Most of the "magic" that Thorinn encounters can be explained as lost technology that he does not fully understand. However, he is also apparently able to do a few "spells" that work despite the machines assuring him that they should not.
- New Eden: The humans first faced the sun going nova, forcing them to push the Earth to a further orbit. Then, internal squabbles caused the structure of society to break down further until the remaining governing humans were forced to turn the task of keeping humanity safe over to the machines. The machines have since created a variety of environments in which to reintroduce life, tuned to their wellbeing. The metaphor of the Garden of Eden is even continued in that Thorinn brings with him knowledge and technology which proceeds to damage the carefully conserved environments.
- Turned Against Their Masters: A rare benevolent case in that the engines are still trying to save humanity. They just believe that the best way to do this is to prevent sentient life from getting too smart and introducing pain into the garden. They're still willing to listen to humans in the chain of command, but they attempt to avoid any such human, for the good of humanity.