By Leon Neyfakh | BOSTON GLOBE, JUNE 24, 2012

A finished basement can be a beautiful thing. With the right accoutrements and enough effort, what might otherwise be a damp, empty space lined with concrete can be turned into a cozy playroom, or a den, or an office and gym. Properly planned, the basement can become an integral part of a household, even a kind of engine that powers it from below.

The same is true for the far larger basement that all of us share: that vast space that exists under our feet wherever we go, out of sight and out of mind. Those of us who are city-dwellers already keep a lot of stuff down there—subway stations, sewer pipes, electrical lines—but as our cities grow more cramped, and real estate on the surface grows more valuable, the possibility that it can be used more inventively is starting to attract attention from planners around the world.

“It used to be, ‘How high can you go up into the sky?’” said Susie Kim, of the Boston-based urban design firm Koetter Kim & Associates. “Now it’s a matter of, ‘How low can you go and still be economically viable?’”

A cadre of engineers who specialize in tunneling and excavation say that we have barely begun to take advantage of the underground’s versatility. The underground is the next great frontier, they say, and figuring out how best to use it should be a priority as we look ahead to the shape our civilization will take.

“We have so much room underground,” said Sam Ariaratnam, a professor at Arizona State University and the chairman of the International Society for Trenchless Technology. “That underground real estate—people need to start looking at it. And they are starting to look at it.”

Read on.