Flatterland

Seen from space, it was a strange world, with the austere beauty of a page from
Euclid. In fact it was a page from Euclid, geometry made flesh: a sprawling,
humming world of two-dimensional shapes. Flatland. A land of lines, triangles,
squares, polygons, circles ... people, of their own kind. They lived polygonal
lives, ate polygonal food, drank polygonal drink, made polygonal love, bore
polygonal children, and died (polygonally) in a two-dimensional universe - and
never thought it the least bit curious. Their flat world was all they could see, all
they could hear, all they could feel. To them, it was all there was.
As long as nothing disturbed that perception, it was true.

But times were changing in Flatland.

—first paragraph, chapter one (and codad at the end)

Flatterland is a 2001 novel by Ian Stewart. It is a Spiritual Sequel to the 120-year-prior novel Flatland. It follows Vicky (the great-granddaughter of Flatland's protagonist) on her tour of the Mathiverse.

Tropes used in Flatterland include:

A Worldwide Punomenon: Most things in the Mathiverse.
Lies to Children: It's meant to be educational, but also entertaining, so the author doesn't stand on detail if it would get in the way of the story (which was a criticism of Flatland, although also a strength).

Vikki started to pick up the junk that had tumbled across the cellar floor, stuffing it back into the now rather battered boxes. She had almost finished when she noticed a tattered book. (More properly, it should be described as a scroll, for on Flatland books are written on lines, not flat sheets, in a kind of Morse code; and the way to store a line compactly is to roll it into a spiral... I can’t keep explaining this kind of thing to you, my Planiturthian readers. So if I use a Planiturthian term that seems not to make sense, for instance, having Vikki—who is a line, for heaven’s sake—pick something up or carry something, you’ll just have to assume that there is some Flatland equivalent.

Spiritual Sequel