The proposed talk is an amalgamation of two views on sensory deprivation and extended periods of darkness. First view is objective – an exploration of history of sensory deprivation practiced by humans in the past and which of these practices are available today. The main focus is on so called dark or darkness retreats – their place in rituals and spiritual traditions, physiological changes occurring in the body and in the brain in different stages of light deprivation, changes in perception, mind altering mechanisms and similarities to states induced by the use of psychoactive plants. Sensory deprivation or isolation tanks are also mentioned, although only marginally. Second view is subjective – a detailed personal account from ten days long darkness retreat which was approached as a psychedelic experience. The three stages common in a traditional approach to a psychedelic experience – preparation, the experience itself and integration – are discussed.