In expensive and crowded downtown Vancouver, a historic piece of real estate sits empty. It's been largely out of sight for decades, and now it's about to vanish.

A 2,400-foot tunnel that runs from the city's behemoth main Canada Post office on Georgia Street to the Waterfront train station, an early example of mail-delivery technology rendered obsolete, is to be filled in, sealing off a piece of Vancouver's history.

The tunnel's demise comes 54 years after it was opened as a marvel of Canada Post future thinking, and almost 50 years after new technology turned it into an expensive and quaint anachronism. This week, Canada Post said it was disposing of another expensive relic: urban home delivery. The postal agency's once-central task of getting messages to people by hand will also fade into history over the next five years.

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The decision to fill in the tunnel has dismayed a cluster of researchers and heritage advocates, some of whom have been arguing that the tunnel is a valuable asset.

"I wish I had a tunnel like that outside my office," says Stephen Mooney, the executive director of Cold Climate Innovation in the Yukon, who had a series of discussions with Canada Post and the City of Vancouver about using it for experimental farming with artificial light. "That's prime real estate."

He and others say tunnels like this one – bored through bedrock, solid and strong, and in the middle of a city filled with creative entrepreneurs – offer a golden opportunity for someone to discover how to grow crops in hostile climates.

Mayor Gregor Robertson walked the tunnel last month in an effort to see for himself the passage he had always heard about. He will likely be the last non-engineer to enter: He was allowed down only after negotiations with Canada Post and extensive safety procedures were put in place for the unventilated space.

Mr. Robertson acknowledges the city has an option to take over the tunnel, "but it would be an enormous expense … to dig it out and reinforce it."

"It's definitely at the end of its lifespan – 60-year-old concrete that's not reinforced, lots of water."

Mr. Robertson says he's also heard the ideas of how to keep the tunnel, but in the end, he says, none of them had "serious financial rigour" and "looking at how far gone [the tunnel] is, it would be very complicated."

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When Vancouver's massive Canada Post building was being planned in the 1950s, the intention was to signal to the world the city's future as the major transfer point between the western edge of Canada and the world beyond.

"It was a massive investment, but the country was catching up on infrastructure after the war. Vancouver was growing and, in that sense, it was quite foresighted," says Donald Luxton, one of the city's heritage experts. The International Style building was the largest welded-steel structure in the world at the time and included a helicopter pad on the roof.

The tunnel was to run from the new building on the cheaper, eastern end of the city's business district, down to the CPR train station on the waterfront. The station and waterfront were the arrival points for mail and parcels from ships in the harbour and trains from the north, east and south.

Conveyor belts monitored by a man on a bicycle would efficiently whoosh bundles of mail up to the building for sorting and delivering, while other bundles would sail back to the train station for delivery across Canada or overseas.

But, like many institutions since, Canada Post didn't grasp how quickly technology would change.

The first plane carrying mail took off in 1918. Daily air-mail service between Vancouver and Montreal started in 1939.

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By 1948, any letter weighing less than an ounce was transported by airplane without an extra charge. But heavier mail and parcels still travelled by trains and Canada Post officials imagined that part of the business – which was most of it – would continue.

The tunnel opened in 1959 after five years of digging that cost $1.6-million. Within months, the postmaster-general, William Hamilton, admitted that mail handling had changed two years earlier, says John Atkin, a city historian who researched the history of the tunnel for tours he conducted through it as recently as 2005.

The tunnel was used for mail delivery until 1965 and then abandoned. The conveyor belts were stripped out and it became a city curiosity, occasionally open for film crews – check out Friday the 13th, Part VIII or The X-Files, various episodes – Halloween parties and tours.

When Canada Post sold the building last year to the B.C. pension fund, the British Columbia Investment Management Corporation, the tunnel turned from a curiosity to a liability for legal and engineering minds at the city.

The head of the city's engineering department, Peter Judd, confirmed that Canada Post asked to terminate its 100-year lease of the tunnel and the city has asked the post office to pay the $1.3-million cost of filling it.

"It has no ventilation, no water, no access. It seems a shame but … if we were going to keep it, we would have to do that maintenance, spending a hundred grand a year for something out of use since the 1960s."

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Richard Shannon is a Vancouver-based technology entrepreneur who is currently working on systems to grow food in harsh climates like Dubai or the Arctic. He describes the tunnel as a "pretty woman to me."

"If Canada Post doesn't want the tunnel, we'll take it. It's literally a 10-acre farm," he says. "It's all concrete-lined, it's in good shape."

Mr. Shannon, who has bombarded city engineers and politicians by e-mail and phone for the last month in an effort to save the tunnel, says he has offered the city a $3-million bond – double the cost of filling the tunnel – to try to persuade officials to keep it open and allow it to be used for experimental farming.

He's made the argument that it's an ideal environment to try growing plants and even salmon in artificial light. Having it in central Vancouver is key, because "you'd be able to pull from all the downtown knowledge workers."

Mr. Mooney, at Cold Climate Innovation, and Simon Fraser University's Professor Mark Roseland say the idea of using the tunnel for farming is sound.

"Saskatchewan has used [potash-mine] tunnels for years to grow fruit trees," Mr. Mooney said. "It's not a new concept."

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A 2,400-foot tunnel that runs from the city's behemoth main Canada Post office on Georgia Street to the Waterfront train station is to be filled in, sealing off a piece of Vancouver's history. See the full story here.