"A Separate Reality" is a book by Carlos Castaneda that explores the teachings of Don Juan Matus, a Yaqui Indian sorcerer. The narrative follows Castaneda's experiences as he learns about perception, reality, and the use of hallucinogenic plants to expand consciousness. The book delves into the concept of multiple realities, suggesting that ordinary perception limits understanding. Castaneda describes various practices and lessons from Don Juan, emphasizing the importance of personal experience in grasping deeper truths about existence and the nature of reality.