Godel, Escher, Bach: An Eternal Golden Braid
This book changed my life. No joke - the deep, lyrical, thinking about recurring patterns, mother nature, the human brain and some underlying mathematics is simply sublime. The book is a tome - and at times I had to work through it like a textbook, using pen and paper to follow along with the maths but I found so utterly rewarding. I can't recommend it enough
-- @tomcritchlow, July 2015.