I recently had the opportunity to experience being in an isolation tank (also commonly known as a sensory deprivation tank), which is a lightless, soundproof tank in which subjects float in salty water (denser than human body) heated to skin temperature. These tanks are used to test the effects of sensory deprivation and also for meditation, prayer, and relaxation, and in alternative medicine.

Robert A. Johnson, Jerry M. Ruhl, Living Your Unlived Life