The book reveals the secrets of alchemy encrypted in the civil architecture of old France. Fulcanelli, more than anyone else, paid attention to the practical issues of traditional science, bringing together its various parts. The author described in detail all the operations of the Work, however, he scattered hints and even direct advice throughout different chapters. So solving the philosophical puzzle-rebus in itself will bring pleasure to the reader. The subject of the book is not limited solely to alchemical secrets. The author takes an extensive excursion into history, linguistics, art history, philology and local history, showing phenomenal erudition. The book is equipped with scientific apparatus and illustrations.