The Woman Who Spent Five Hundred Days in a Cave. I’ll just copy the Browser’s intro, who I got this from, because it’s dead on, and better than anything I could come up with:

Every twist in this tale about a Spanish woman who spent 500 days living utterly alone in a remote cave makes the jaw drop further. Her goal was total disconnection from all human contact, although she did allow security cameras and a panic button in case of emergency. It was “a year and a half inside a sensory-deprivation tank”. She achieved this and, mostly, she thrived