They were sensory deprivation tanks, where users float in salt water in pitch blackness for hours at a time. Invented by National Institutes of Health researcher and neuroscientist John Lilly26 in the 1960s, these tanks were specifically designed to help people shut off the self (since the brain uses sensory inputs to help create our sense of self, by removing those inputs, you can dial down this sense). After Lilly began using these tanks to explore the effects of LSD and ketamine on consciousness, they fell out of favor with the establishment and devolved into a countercultural curiosity.
