Naikan - Structured method of self-reflection developed by Yoshimoto Ishin

"Naikan is a structured method of self-reflection developed by Yoshimoto Ishin (1916–1988) a businessman and devout Jodo Shinshu Buddhist who, as a young man, had engaged in an ascetic 'contrition' (mishirabe) practice involving sensory deprivation through dwelling in a dark cave without food, water or sleep. Wishing to make such introspection available to others he developed Naikan as a less difficult method which he first introduced to young people who had been incarcerated for committing crime and social disturbances. Later the practice was introduced to the general public. Naikan practitioners claim that Naikan helps people understand themselves and their relationships. - Wikipedia"