Many things go wrong when a human spends months alone in a dark cave. Time stills and the body’s rhythms go awry.

Sleep withers to a few hours a night, and menstruation may come to a halt. Enthralling stories, like that of Spanish climber and cave-dweller Beatrice Flamini’s, shed light on what motivates someone to become a cave dweller.

Flamini’s Life as a Cave Dweller

On April 14, Flamini emerged from a cave in the country after spending a record 500 days isolated underground, save for a “technical problem” that forced her to bivouac for eight days on the surface, in a tent. Life underground had taken on its own rhythm of reading, drawing and knitting woolen hats, and taking care of her personal needs. She left her waste at a no-contact collection point and received food in return.

Released from her grotto, she first asked who would pay for a round of celebratory beers.

“I was sleeping, or at least dozing, when they came down to get me,” she told reporters, according to The Guardian. “I thought something had happened. I said, ‘Already? No way.’ I hadn’t finished my book.” Like other record-breaking cave dwellers before her, she had read stacks and stacks, totaling to 60 books. Overall, she called cave life “excellent, unbeatable.”

The Downside of Living in Isolation

Flamini’s GoPro videos share the downsides of living in isolation.

“It’s not that the time passes more quickly or more slowly,” she vents in one video. “[It’s] simply that it doesn’t pass, because it’s always four in the morning.”

In another video, she realizes she has lost something, while hanging from ropes in the cave, and covers her face. “What a terrible day,” she says. “I have been wanting to cry all day.”

What Inspires Someone to Isolate?

Decades before Flamini, an Italian sociologist named Maurizio Montalbini spent a total of two years and eight months underground, by his own count, isolating in caves for various stints (210 days here and 366 days there).

One time, he lived in a little underground setup with running water and electricity and wore monitoring equipment to relay his condition to a team of experts. While underground, he read profusely and munched on walnuts and chocolate as time slipped by, as it did for Flamini.

What inspires these record-setting isolators to attempt such marathons? In a very serious way, they are deleterious to the isolators’ health — social isolation reduces life expectancy by about 15 years, similar to smoking 15 cigarettes a day, according to the National Institute on Aging.

Read More: Social Isolation Increases Risk of Cardiovascular Issues

A Hermit Reveals the Unique Joys of Isolation

While a threat to one’s health, isolation can also be freeing, say modern-day hermits. Brother Rex, a Catholic hermit from the Portland area, follows a daily schedule filled with prayer, church services, spiritual reading and a certain amount of responding to emails.

“One of the most joyful aspects of my life as a hermit is the opportunity God has given me to spend long periods in the silence of solitude,” he says, “to practice being present to God and to my neighbor through prayer.”

A hermit in his own right, Maine resident Christopher Knight spent 27 years living alone in a tent in the woods, ending in 2013.

According to Michael Finkel, who wrote The Stranger in the Woods about Knight, “He was never for a moment, in all 27 years, bored. He was never lonely. He said that he felt almost the opposite of that. He said he felt utterly and intricately connected to everything else in the world. It was difficult for him to tell where his body ended and the woods began.”

Read More: Humans Evolved To Be Lonely

Spelunkers at Home in Caves

While Knight felt almost a physical force pulling him into isolation, Montalbini once told a reporter who asked if he preferred life underground, “Are you trying to be funny? I’m not going back in there. I need the sun. I used to dream about the dawn. It’s an experience I would not repeat.”

And yet he later climbed into Italy’s Grotta Fredda (“cold cave”) in 2006 and stayed there for 235 days, shorter than the three years initially planned.

Like Flamini and Montalbini, spelunkers often feel uniquely at home in caves, where our ancestors lived for at least two million years.

Flamini grew fond of her little home, but the process took some effort.

“I am where I want to be,” she told herself and acknowledged that what she was missing out on was “part of the project. There is nothing to do but accept it.”

Read More: Why Alone Time Carries a Stigma