“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.”

The federal government has taken an interest, convening a panel of specialists under the banner of the National Academy of Engineering to produce a report, due out later this year, on the potential uses for America’s underground space, and in particular its importance in building sustainable cities. The long-term vision is one in which the surface of the earth is reserved for the things we want to see and be around—houses, schools, yards, parks—while all the other facilities that are needed to make a city run, from water treatment plants to data banks to freight systems, hum away underground.