Psychedelic:
Adjective:

• of or noting a mental state characterized by a profound
  sense of intensified sensory perception, sometimes
  accompanied by severe perceptual distortion and
  hallucinations and by extreme feelings of either euphoria
  or despair. The later years of the 1960s saw the rise in more avant-garde
  music as artists and musicians began to experiment with
  mind altering substances.

Beginning with the hippie movement in America and
rapidly spreading across the Atlantic to Britain, this period
in music saw bands such as The Beatles - free from their
touring commitments - together with The Rolling Stones,
Pink Floyd and many others make use of sensory altering
concoctions to reach new heights of artistic creativity.

This is the story of those years.