Figuratively speaking, C. G. Jung, M.D. (1875-1961), the Swiss psychiatrist and psychological theorist, could be described as visiting the underworld of his psyche periodically over a number of years. In his self-experimentation, he visited the underworld of his psyche through self-induced hallucinations -- visual and auditory hallucinations.
Self-inducing hallucinations is a potentially dangerous practice, and I do not recommend it. Instead of doing it for ourselves, we can read Jung's elaborate report of his experiences.
In 2009, Norton published Jung's RED BOOK: LIBER NOVUS, expertly edited by the historian Sonu Shamdasani, translated by Mark Kyburz, John Peck, and Sonu Shamdasani. It is a handsome over-sized book that includes many informative footnotes by Shamdasani. Jung's RED BOOK contains many of his works of art based on his visual hallucinations and the "fair" copies of the texts he produced in calligraphy based on his auditory hallucinations. In addition, some other material Jung recorded in connection with his encounter with the unconscious is included in three appendices.
In addition to the over-sized book, Norton also published the regular-sized book THE RED BOOK: LIBER NOVUS; A READER'S EDITION (2012). Both books contain the same textual material, but arranged differently. However, Jung's paintings are not reproduced in the READER'S EDITION.
In 2013, Norton published LAMENT OF THE DEAD: PSYCHOLOGY AFTER JUNG'S RED BOOK, which consists of the transcribed and edited transcripts of 15 conversations between James Hillman and Sonu Shamdasani, and endnotes prepared by Shamdasani and an index. (Hillman died in the fall of 2011. But he had reviewed the transcripts before his death.)
The main title of Hillman and Shamdasani's book is wording from part of the RED BOOK (page 297; READER'S EDITION, page 344).
The subtitle of their book, "Psychology after Jung's RED BOOK," announces the theme of their conversations. But here's how Hillman paraphrases the theme of their conversations: "What is the RED BOOK telling us about the psyche? What came to Jung is this book?" (page 38).