Foremost book available on polytopes, incorporating ancient Greek and most modern work done on them. Beginning with polygons and polyhedrons, the book moves on to multi-dimensional polytopes in a way that anyone with a basic knowledge of geometry and trigonometry can easily understand. Definitions of symbols. Eight tables plus many diagrams and examples. 1963 edition.
Harold Scott MacDonald "Donald" Coxeter (1907-2003), CC, FRS, FRSC was a British and later also Canadian geometer. He is regarded as one of the greatest geometers of the 20th century.
I bought this from an interest in pattern and polyhedra as it is an established classic, delving into higher dimensions. I can't deny that it is classic and definitive, but it is very much a textbook aimed at those doing maths as a career or postgraduate study. For my purposes, half an hour on wikipedia was more fruitful to get a practical on-hands overview of higher dimensional polytopes.
For this alone: "... in attempting to do so, however, we seem to peep through a chink in the wall of our physical limitations, into a new world of dazzling beauty. Such an escape from the turbulence of ordinary life will perhaps help to keep us sane."