Doors of Perception and Heaven and Hell

The Doors of Perception is a 1954 book by Aldous Huxley detailing his experiences when taking mescaline. This short book is considered to be one of the most profound studies of the effects of mind-expanding drugs and what they teach about how the mind works.
The title comes from William Blake's The Marriage of Heaven and Hell:
"If the doors of perception were cleansed,every thing would appear to man as it is, infinite. For man has closed himself up, till he sees all things through narrow chinks of his cavern."