Sphereland
A sequel to Edwin Abbott's Flatland, written by Dutch author Dionys Burger and first published in the 1960s. It follows a descendant of the original Square as he tries to convince a flat, two-dimensional world that space itself can curve and that the universe is expanding. Where Flatland used geometry to satirize Victorian society, Sphereland leans into the science, using the same flat-creatures conceit to explain non-Euclidean geometry and general relativity in plain terms. For a book club it reads as a short, playful thought experiment that makes hard physics feel approachable.