In 1964, Timothy Leary, Ralph Metzner, and Ram Dass published a book they wrote entirely while tripping: The Psychedelic Experience: A Manual Based on The Tibetan Book of the Dead. You can read it for free on Psychedelic Frontier.
The Tibetan Book of the Dead is a funerary text that dates back to the 8th century, and is intended to guide one through death, and its associated experiences.
From Psychedelic Frontier:
Timothy Leary, Ralph Metzner, and Richard Alpert (aka Ram Dass) literally wrote the book on tripping. In 1964, they published The Psychedelic Experience: A Manual Based on The Tibetan Book of the Dead, which captured the imagination of psychonauts everywhere and laid the groundwork for all psychedelic literature to come. As the title indicates, this guide was inspired by the Bardo Thodol, re-interpreting the classic Tibetan text as a guide for ego death.
As the first spiritual guide to using psychedelics, The Psychedelic Experience was revolutionary, and continues to influence all aspects of psychedelic culture. It’s hard to imagine the wide variety of trip guides available today if it weren’t for this pioneering book. It’s still worth a read today.