Yesterday I read Graham Hancock's Supernatural: Meetings with the Ancient Teachers of Mankind (2007). Basically, without coming to any conclusion or positing any credible theory, the purpose of the book is to point out some pretty astounding similarities between ancient pre-historic cave drawings, traditional accounts of fairy lore, modern scientific experiments with DMT, and alien abduction testimonies. Shamans from many world cultures have used combinations of plants to communicate with "higher-beings" of some kind who teach them things. ...
If you're interested in religious mythology, astrological symbolism, or supernatural folklore, grab my book Gods of Myth and Man. You can go buy it on Amazon.