Fulcanelli and Le Mystère des cathédrales
The legends about Fulcanelli postdate the book and rest on later, separate testimony: the warning about atomic weapons on Jacques Bergier's account of a 1937 meeting, published in 1960, and the longevity on Eugène Canseliet's claim to have met the long-vanished master in Spain in the 1950s. His identity remains unconfirmed.
Fulcanelli, Le Mystère des cathédrales (1926); Louis Pauwels & Jacques Bergier, Le Matin des magiciens (1960); Kenneth Rayner Johnson, The Fulcanelli Phenomenon (1980)
A 1926 book reading Gothic cathedral carvings as coded alchemical instruction, published under a pseudonym whose real identity has never been confirmed.