This is the second book by the Shulgins which mix their autobiographies with the subjective effects of new and well-studied psychadelic drugs. It lies on the cusp between top-level synthetic chemistry and guru-level self development, and is amust for anyone interested in self development or recreational drug usage. Highly recommended, but it would make more sense if one reads PIHKAL first.
Contains Book I & Book II- the chemistry, freely available online.