In this monograph, I relate findings from more than 30 years of experiences and observations with this substance, in various user groups and individuals, both in the US and in Europe. I use the term underground in referring to the explorations with these substances, in the sense that they were hidden - out of respect for the restrictions and prohibitions of mainstream culture.These are ethnographic field reports: first-hand observations from an underground sub-culture, accompanied by the experiences of a selected number of participant-observers. It is important to recognize that in research with these and other so-called psychedelic or entheogenic substances, one cannot limit the observations and reflections solely to their physical and psychological effects. As most of the people cited here emphasize, the experiences with these substances at times can go far beyond their physical and psychological effects into the deepest and highest dimensions of our existence, both the cosmic and the spiritual.