If you think the urban sprawl of Tokyo looks impressive from above, wait until you factor in the areas below ground. With demand for commercial and residential space increasing on the surface, more and more developers are exploring ways to utilize space underground.

Hundreds of curious sightseers attended a preview of Tokyo's latest underground passageway — a 900-meter tunnel in Minato Ward connecting Shimbashi to Toranomon — on March 23. More than 38,000 vehicles are expected use the Tsukiji-Toranomon Tunnel every day, bypassing one of the capital's busiest business quarters and alleviating traffic congestion above ground.

Building the four-lane road, dubbed "MacArthur Road" after U.S. Gen. Douglas MacArthur, who led the Allied Occupation of Japan after World War II, certainly hasn't been easy. Construction work was originally slated to start in 1946 but the project fell behind schedule after running into delays related to land-use planning. Indeed, structures that already exist underground forced developers to take the road right through Toranomon Hills skyscraper's basement floor. "We wanted to preserve the surface of the area as much as we could, since there are locals who hold a strong attachment to the district," says Takeshi Oyagi, chief of the Tokyo Metropolitan Government's Urban Development Office, adding that it was "not technically difficult" to run a road through the basement of a 52-story building.