Egan (The Arrows of Time, 2014, etc.) specializes in inventing seriously strange worlds; this one might well be his weirdest yet.
Seth, a Walker, like all his kind can only orient his body in an east-west direction and is blind to what lies north or south. Inside his skull lives Theo, a cylindrical symbiont called a Sider, who projects infrasound pulses north and south and observes the reflections. They can speak to each other and see what the other sees. Like all living things here, they and their fellows must migrate perpetually to follow their sun’s bizarre orbit and the wobbling habitable zone it generates. What? Well, our universe consists of three space dimensions and one of time; this world has two space dimensions and two of time, so instead of a sphere they’re on a hyperboloid. This isn’t the half of it; water, for instance, runs up any slope of less than 45 degrees. The city where they live, Baharabad, must constantly be disassembled at one extreme and reassembled at the other (though we never get to see this happening). Seth and Theo are surveyors, scouting ahead to map a safe path for the migration. But then their expedition encounters a seemingly bottomless, boundless chasm. All this doesn’t sound too bad in synopsis. The problem is, it’s counterintuitive, so downright odd that it’s impossible to visualize the inhabitants, their surroundings, or what’s going on. Knowing what the mathematical justification is doesn’t help. There are plenty of other issues too. How did Walkers and Siders survive independently, as it seems they did, before becoming symbionts? Why would Walkers have such convenient holes in their skulls? It’s not even particularly original: back in 1974 Christopher Priest envisioned something similar (Inverted World) with much greater success.
Hard to imagine much of an audience outside math brainiacs and Egan enthusiasts.