For him, that meant living deep in a Swedish forest, an hour and a half walk from the nearest train station — a trip that could take four hours during the winter, when the snow was deep — with a couple of other similarly inclined individuals who would come and go. He had a cellphone, which he charged with a small solar generator and used to call his family and his girlfriend, a college student who visited him every few weeks.

His diet was not for the fainthearted. Along with perch and pike from nearby lakes, he ate wild plants like nettles, berries and tubers, as well as mice and rats. He couldn’t hunt larger game because he didn’t have a gun — to purchase one, he would have had to provide an address — but he began studying how to make a bow and fletch arrows. On infrequent trips to town, he would scavenge for unspoiled food in the trash.

“We live in a world where everything is so specialized, now people don’t know how to make anything, they don’t know how to survive,” he said, speaking by cellphone from the forest. “I’m not completely self-sufficient, but I’m learning.”

Every aspect of his daily routine was essential to his survival. “I have to collect firewood, rather than do some job that I have no idea what is the point, which I hate, and from which I am completely alienated,” he said. “Everything in my life feels full of meaning.”

Recently, though, Mr. Griffith-Jones left the forest, having decided that the lifestyle was not as sustainable as he had hoped, mostly because “women weren’t willing to live there,” he said, “or raise up children in the forest.” He is now trying to start an ecologically minded commune on a farm nearby.

DAVID GLASHEEN, 66, likened his experience of living alone to “going to the moon.”

“Everything you’ve ever learned means nothing till you come to a place like this,” said Mr. Glasheen, who lives on Restoration Island, off the northern coast of Australia, with his mixed-breed dog, Quasi, and has been there since 1996. “It’s the pinnacle of privacy.”

An entrepreneur who said he has worked in a number of fields — including mineral exploration, food services and toys — he had suffered a series of financial losses and divorce when a girlfriend suggested escaping to an island in the early 1990s.