The Doors of Perception

Aldous Huxley's 1954 account of his mescaline experience — arguing that psychedelics work by reducing the brain's filtering function, allowing more of reality (which Huxley associated with Bergson's Mind at Large) to enter consciousness — the founding text of the psychedelic intellectual movement.

Proposed the filter theory of consciousness — the brain doesn't produce consciousness but filters it, reducing the infinite to what is biologically useful — and that psychedelics temporarily reduce this filter, giving access to wider consciousness that mystics access through other means.