"All over the world, there were people who, for reasons they could not quite articulate, had fallen into a kind of fugue state and dedicated their lives to digging underground — a whole case file of Mole Men."

"There was Lyova Arakelyan, a man in rural Armenia who, while excavating a potato cellar beneath his home, became transfixed, and spent the next three decades digging winding tunnels and spiral staircases. To those who asked why, he only explained that each night he heard voices in his dreams telling him to dig. And the entomologist Harrison G. Dyar, Jr., who excavated a quarter mile’s worth of tunnels beneath two separate houses in Washington, D.C. When the tunnels were revealed in 1924, after a car fell through the street, Dyar told the press, 'I do it for the exercise.' And an old man in the Mojave Desert, William 'Burro' Schmidt, who spent thirty-two years pickaxing a 2,087-foot-long tunnel into the side of a solid granite mountain. ('Just a shortcut, I suppose.') And a young man named Elton Macdonald, who covertly excavated a thirty-foot-long tunnel beneath a city park in Toronto, which caused a city-wide panic after the police announced the tunnel as a potential hideout for terrorists. When Macdonald revealed himself as the burrower, he could only explain, 'Digging relaxes me.' And then Lord William Cavendish-Scott-Bentinck, a nineteenth-century duke, who, along with a crew of laborers, hollowed out an entire tunnel metropolis beneath his estate, complete with an underground library, a billiards room, and a ten-thousand-square-foot underground ballroom made entirely of clay, which the duke used as a private roller-skating rink."

From "Underground: A Human History of the Worlds Beneath Our Feet" by Will Hunt. I highly recommend this book, which I read right after another book with the same title, different subtitle, "Underground: The Tokyo Gas Attack and the Japanese Psyche," by Haruki Murakami.

Is there some natural urge to burrow underground? Will Hunt writes: "Physiologically speaking, there is no environment so intolerable as a tight, dark, underground enclosure, where oxygen is scarce. To burrow is to experience claustrophobia in its most crystallized form, like enclosing yourself in a tomb. And yet, throughout history, in every corner of the world, we have burrowed...."