n. An extremely long or exceptionally well built tunnel.
Also Seen As
In the past quarter century, officials have discovered a hundred and eighty-one illicit passages under the U.S.-Mexico border. Most have been short, narrow “gopher holes” just big enough for a person to crawl through. Sinaloa specializes instead in infrastructural marvels that federal agents call supertunnels. Agents estimate that a single supertunnel takes several months and more than a million dollars to build.
—Monte Reel, “Underworld,” The New Yorker, August 03, 2015
Sir Albert Bore, leader of Birmingham City Council, said that could take the form of joining up the tunnels or even creating a motorway under the city.

Dr Pat Hanlon, a transport expert at the University of Birmingham, said a "supertunnel" could not only improve congestion, but open up parts of the city for building, allowing key areas such as Great Charles Street and the Colmore business district to be joined up.
—“Birmingham outlines £4bn tram and bus plan,” BBC, November 13, 2014
He said the tunnel — like the two most recent “supertunnels” in the region, which were discovered in late 2011 — was shut down before any narcotics reached the market in the United States, which he called a major blow to the cartel.
—Liam Dillon & Ian Lovett, “Tunnel for Smuggling Found Under U.S.-Mexico Border; Tons of Drugs Seized,” The New York Times, October 31, 2013
2003 (earliest)
There are stories about a network of tunnels linking the Rottnest Battery with the Army Depot on Rottnest Island. There was also a "super rumour" of a super-tunnel that linked Rottnest Island with Buckland Hill Battery on the mainland.
—Peter Dunn, “Rottnest Island Tunnels, Western Australian during WW2,” Australia @ War, May 13, 2003
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