The Old Book Smell
Lignin, the stuff that prevents trees from turning into the weeping kinds, is a polymer made up of units that are closely related to vanillin. When made into paper and stored for years it breaks down and smells good. Which is how divine providence has arranged for second-hand bookstores to smell like good quality vanilla, subliminally stoking a hunger for knowledge in all of us.
From Perfumes: The Guide