Flatterland

Even though the name is very similar to Flatland, this book is much more fun. It talks about hyperbolic space, how there could be a hundred and one dimensions, what 1.5 D means, Topology, Wormholes, Paradoxes, Quantum Mechanics and much more. It contains several difficult concepts, so I would recommend you to only start reading it after you turn 11. By the way, it is based on Flatland, so I recommend you to first read Flatland.