The Big O isn’t much of a baseball park, with dim light and long-distance sight lines. The venue’s echo makes it even worse for concerts. The stadium can be fine for occasional football or soccer games – provided the teams can fill the place with fans to turn drab concrete festive. Plus, those balls are big enough to be seen from far away.

When it comes to the usual vocations of a massive domed coliseum, Montreal's Olympic Stadium is a well-known, barely serviceable white elephant.

It is also, however, the perfect trap.

Quebec's provincial government, owner of Canada's biggest stadium, will spend $200-million to $300-million to replace the Big O's 20-year-old roof, a public-safety hazard peppered with 8,000 patched holes. On hearing the news, critics familiar with the stadium's flaws, the $32-million the province spends each year to run and fix it, and the $1.5-billion, 30-year saga to pay for construction, immediatey asked, "Why not just tear it down?"

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The answer irritates many sports fans, taxpayers and economists: Montreal's Olympic Stadium is preserved thanks to a combination of inertia, nostalgia, civic pride, cheap land, small-scale usefulness, solid concrete and the province's preference for a predictable annual budget over fear of runaway demolition and redevelopment costs.

More than $100-million has been steadily sunk into fixing up the stadium in the past decade and a similar amount is being spent over the next 10 years – not including the roof.

"When you add up all the factors, there really is no choice but to put on a new roof. It's unavoidable," says Julie Boulet, the Quebec Tourism Minister, who is in charge of the stadium. "When you add up all the elements, logic dictates it."

Cedric Essiminy, public relations officer for Montreal’s Olympic Stadium, gives a tour of the roof structure on Nov. 23, 2017.

While the stadium still hosts the occasional soccer and baseball game, its two major vocations are as tourist attraction and landlord for occasional events and a number of permanent tenants. The main bowl is only usable half the year because the roof risks collapse with even a three-centimetre snowfall. A new roof should fix that.

With its landed-spaceship look and leaning tower offering the best view of the city, it draws hundreds of thousands of visitors each year.

"There's no doubt that, from an outside point of view, it has iconic value as a symbol of Montreal," said Elsa Lam, editor of the upcoming book Northern Building: Canadian Architecture, 1967-2017, which has a chapter dedicated to the stadium. "I don't think you'd get architects out with placards to save it from demolition, but it is special."

Since embarking on a relaunch plan in 2012, stadium managers have carved out useful spaces inside the incredible hulk.

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Beneath the leaning tower, the province renovated five of the stadium's six Olympic pools and built a national training centre for elite amateur athletes.

A view of the tower, under repair, at the Olympic Stadium in Montreal on Nov. 23, 2017.

On a recent weekday, aspiring Olympian fencers thrust and parried, judoka wrestled and ordinary gym rats lifted weights in the spacious and bright training rooms beneath the immense grey, cantilevered pillars. Young athletes tried out for the national synchronized swim team in one pool while several dozen seniors exercised in another. The stadium has become one of the nicest recreational hubs in the city for Hochelaga-Maisonneuve, one of Montreal's poorest neighbourhoods.

An elevator ride leads to tower floors that were dormant for 30 years and are now being renovated into a workplace for 1,000 Desjardins Group credit-union employees. The stadium has 700 other tenants, many of them non-profit and sporting organizations.

Despite the hum of activity, the stadium will never pay for itself, the chief manager readily admits. "Because we have no sports teams, a lot of people in Canada and Quebec think nothing happens at the stadium," said Michel Labrecque, president of Parc Olympique, the provincial agency that runs the stadium. "But we're holding trade shows and shooting movies in here 150 to 180 days a year. People don't realize it."

In the corridors of power in the stadium and in Quebec City, decision makers firmly believe demolition would be ruinously expensive and would leave a gaping 10-block hole.

One estimate years ago suggested a tear-down could cost up to $700-million, a figure the study author said was a worst-case scenario.

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No stadium demolition in North America has ever cost one-20th of that, but Mr. Labrecque points out that no other stadium was built with high-tension concrete and cables, a 165-metre tower, a 4,000-spot underground parking lot, unknown levels of asbestos to decontaminate and a Metro line running beneath it all. "It's not going to get done for $50- or $100-million, that much I can guarantee," Mr. Labrecque said.

Unlike politicians and civil servants, economists seem more ready to knock it down. Andrew Zimbalist, a U.S. sports economist, says spending hundreds of millions of dollars to maintain the Big O's current use "is silly."

"It might cost a lot to tear down but it costs an enormous amount to operate," Dr. Zimbalist said. "If major-league baseball comes back, it won't be in the Olympic Stadium. Losing a trade show or two a year doesn't justify $32-million a year and hundreds of millions more for a roof. You could build a pretty nice pool and gym for that."

Dr. Zimbalist said pouring more public money into the Big O can only harm the long-term prospects of bringing back major-league baseball, which will require a modern downtown ballpark that would probably need public funds to get off the ground. "The baseball commissioner was very clear you'd need a new stadium, something modern and better located. If you want baseball you should tear it down and bite the bullet," Dr. Zimbalist said.

Montreal’s Olympic Stadium has become an enormous white elephant, but officials have decided the estimated tear-down cost of up to $700-million rules out that option.

The stadium may live forever on inertia since it was born from it. In 1912, the old municipality of Maisonneuve set aside the site for a sports and recreation area. In a twist befitting the stadium nicknamed the Big Owe, Maisonneuve went broke and was absorbed by Montreal.

Camillien Houde was elected mayor of Montreal in 1928 and immediately started failed lobbying attempts to host the Olympics and build a stadium. He broke ground in 1938 after winning a bid to hold the 1942 British Empire Games, and then war cancelled everything. The sloped spot was used for sledding.

Jean Drapeau won the mayor's chair in 1960, bringing ambition and insouciance about cost. The successful Expo 67 set the stage for the winning 1976 Olympic bid.

The reason for the stadium's endurance also lies in the heart of many Quebeckers, who have come to accept that Montreal's biggest landmark is an ambitious but flawed reflection of where they live. A poll conducted a few years ago by Léger showed about 80 per cent of Quebeckers believed the stadium is an important part of Montreal and that the roof should be replaced. With renovations, regular inspections and a new roof, engineers project the stadium will function until 2066.