The city winched north toward optimum
The city Earth, about a thousand people, is hauled along a handful of rails that are constantly torn up behind it and relaid ahead. Its guilds (Traction, Track, Bridge-builders, Futures, Militia) keep it near a moving point called 'optimum'. Helward Mann travels south into the 'past' and experiences time dilation, and he watches local women brought from outside grow wider and flatter, then are crushed into a flat disc. At the end the city reaches the sea, and Elizabeth Khan, a woman from outside, tells Helward it is on ordinary Earth, and that the hyperbolic world exists only in the perception of the citizens, a distortion created by the 'Destaine field' generator their founder built.