• Building landmarks like the Statue of Liberty involved huge feats of engineering. • It took 14 years for the Sydney Opera House to be completed. • Antoni Gaudí's Sagrada Família in Barcelona remains a work in progress.

They might be instantly recognizable today, but these iconic structures were once just piles of steel and stone.

In some cases, famous landmarks, like the Statue of Liberty or the Eiffel Tower, took years, millions of dollars, and great feats of engineering to be constructed.

The Sydney Opera House — whose iconic "shells" are covered in one million tiles and were built using cranes designed for the job — took 14 years and AU$ 102 million to complete, just in time for Queen Elizabeth II's visit to Australia in 1973.

Meanwhile, Antoni Gaudí's famous Sagrada Família i

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