What was the book that opened your mind to the beauty of mathematics? Of course, I am generalising here. It may have been a teacher, a theorem, self pursuit, discussions with family / friends / colleagues, etc. that opened your mind to the beauty of mathematics. But this question is specifically about which books inspired you.

For me, Euler, master of us all is right up there. I am interested in which books have inspired other people.
Gödel, Escher, Bach by Douglas R. Hofstadter
Dungeons &amp; Dragons, Basic edition player's manual.