One thing is certain: The mind is vaster and more fluid than our ordinary, waking consciousness suggests. And it is simply impossible to communicate the profundity (or seeming profundity) of psychedelic states to those who have never experienced them.
Waking Up: A Guide to Spirituality Without Religion
It is a 2014 book by Sam Harris. Harris discusses a wide range of topics including secular spirituality, the illusion of the self, psychedelics, and meditation. He attempts to show that a certain form of spirituality is integral to understanding the nature of the mind.