The Sydney Opera House - one of the most recognisable buildings in the world - was opened by Queen Elizabeth II on October 20, 1973.

Its sail-like shell design pushed the boundaries of engineering during its 14 years of construction, and the building came in 14 times over its original budget at $102 million.

In the 1950s, Danish designer Jørn Utzon had emerged the winner of a global contest to design the national opera house at Bennelong Point with his striking concept.

But Sydney Harbour would have looked very different if one of the other designs had been given the nod by the NSW government.

Runner-up in the competition went to the Philadelphia Collaborative Group - composed of seven influential American architects who went for a look far different to Utzon.

They took their inspira

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