Sydney “got tapped on the shoulder by a rainbow” when it rejected 232 other architects and picked Jorn Utzon to design the Opera House.
That is how former prime minister Paul Keating explained the crazy-brave decision in 1957 to go with the jaw-dropping designs of a 39-year-old Dane.
Forty years on from the opening of one of the 20th century's most distinctive buildings, and five years since Utzon's death, there is still amazement that curves were chosen over angles.
Thinking outside the box, according to Opera House Trust boss Kim Williams, has delivered a waterfront adornment that is "core to our national identity".
Utzon was sacked over cost overruns and never returned to Australia to see his masterpiece finished. He had to wait until 2003 for the Pritzker Prize as a token of appreciation for a much-loved, much-photographed, much-visited building.
Receiving architecture's highest award, Utzon rightly boasted that the Opera House had become a "symbol for not only a city but a whole country and a continent".
Discussing the nature of that symbol is a national obsession.
Its partner in the harbour is the bridge, which was delivered on time and on budget. When it opened in 1932, it was so futuristic that hardly one-tenth of its capacity was needed.
The Opera House, 14 years in the making and 14 times over budget, is a masterpiece of form but a failure in terms of function.
Work to make it work has been continuous since its opening in 1973.
Danish Crown Prince Frederik and Crown Princess Mary will attend the anniversary concert in late October, when the orchestra will perform Beethoven's Symphony No.9.
Construction workers putting in a new tunnel to try to sort out the building's internal problems will be given the day off, so the banging and clanging will not drown out the orchestra.
Sydney architect Ken Woolley was pilloried five years ago for arguing that it would be cheaper to build a new opera house than to bear the enormous expense and trouble of trying to improve the acoustics of the original.
"Trying to create a new opera theatre inside the present building will inevitably lead to compromise," he said, suggesting an adjacent site for a new hall.
Keating spoke for the many outraged by Woolley's courageous solution to the Opera House's problems.
"A giant box dropped into this space, I believe, has absolutely no merit," he said.
Utzon's defenders argue that changes to the interior came after he left the country, and say he is unfairly blamed for the inadequacies that have Woolley calling for a clean start.
The Opera House is a logistical nightmare for theatre directors. Sets, stages and even performers have to arrive and depart vertically rather than laterally.
In the opera theatre, the brass section in the orchestra pit is screened off from the rest of the ensemble so other players are not deafened. In the main concert hall, there are Perspex "doughnuts" hanging from the ceiling to try to improve the aural experience.
Woolley and others have argued that the Opera House is loved for its exterior, and few would be troubled that opera and orchestral works were taken out of its shell and popped in a purpose-built new space.
Fellipe Mathias de Silva, in Sydney from his native Brazil to learn English, is one of about nine million people who visit the Opera House year.
"It's very different from other buildings," he said when gazing admiringly at Utzon's flawed masterpiece.
"If you come to Australia the first place you need to know is the Harbour Bridge and the Opera House. It's different. It's not square. Most buildings are squares."
Australian author David Malouf, who lived through the 14 years of construction, is more lyrical in his praise of the World Heritage-listed building.
Malouf wrote that the harbour city had recomposed itself around its crowning glory "as if it had been waiting for just this miraculous object to appear and claim its place".
The 40th anniversary of first concert at Sydney Opera House is on October 20
By Sid Astbury