Knowledge of the Higher Worlds and its Attainment
by Rudolf Steiner
1944
This is Rudolf Steiner's guide to the seeker on the path of esoteric initiation. He includes much that would be of use to novices of any mystical belief system, and a lot of tantalizing information about the subtle body, higher planes of existence, and the spiritual encounter with the 'Guardians of the Threshold.' --J.B. Hare