Introduction:
On October 20, 1973, the world watched in awe as Queen Elizabeth II officially opened the shell-shaped marvel that would forever change the landscape of Sydney Harbor – The Sydney Opera House. Reflecting the waves of the ocean, mirrored onto the horizon by its inimitable silhouette and luminous tiles, this iconic structure situated on Bennelong Point continues to epitomize Australia’s creative and innovative spirit.

Event Overview:
Planning for the Sydney Opera House commenced in the late 1940s, with the original design chosen through an international competition in 1956 held by the New South Wales Government. The winner was a then-unknown Danish architect, Jorn Utzon. Utzon employed groundbreaking construction techniques to create the building’s revolutionary design, which resulted in both structural complications and budget overruns that forced him to leave Australia before the completion of his masterpiece.

Greater than the sum of its architectural elements, the Sydney Opera House took 16 years to build, with construction starting in 1959. Initially budgeted at a mere AU$7 million, the Sydney Opera House ended up costing the Australian taxpayers an astonishing AU$102 million. Despite numerous construction challenges, delays, and public controversies, the architectural wonder came to represent not only the city of Sydney but also the entire nation.

Interesting Facts for Kids:
Before the Sydney Opera House was the massive architectural marvel you know today, it was a fortress. Bennelong Point used to be home to Fort Macquarie, built in 1821.
Despite being called the ‘Opera House,’ it hosts more than 1,500 performances annually that include ballet, theatre, symphony concerts, and popular music in addition to opera.

Educational Activities for Kids:
1. Drawing the Sydney Opera House: Children can learn about its unique design by trying to sketch the building. It helps in understanding the abstract geometry of the structure.
2. Virtual Tour: Owing to modern technology, there are plenty of virtual tours online where kids can virtually walk-about the Opera House, learning about its history, architecture, and its cultural significance.
3. Australian Culture Lesson: Teachers can design lessons around Sydney Opera House to give kids an insight into Australian culture and arts.

Conclusion:
Recounting this monumental day on October 20, 1973, continues to cultivate a sense of national pride for Australians and admiration from onlookers worldwide. It emphasizes the long-lasting impacts that architecture and cultural institutions can have on society, embodying the power of persistence, innovation, and collective effort. Today, Sydney Opera House stands as a UNESCO World Heritage Site and a symbolic representation of human ingenuity in creating a space that simultaneously serves artistic expression and societal unity.

References:
1. State Records. The Sydney Opera House. The State Records Authority of New South Wales, 2012
2. Murray, Peter. The Saga of the Sydney Opera House. Spon Press, 2006
3. Freeland, J.M. The Sydney Opera House. Lond. Elek Books, 1973
4. Sydney Opera House Trust. A heritage of Australia. 2005. Sydney Opera House Trust, Australia.
5. Stübe, Katarina. Jorn Utzon and the Sydney Opera House. Indigo, 1998.
6. “Sydney Opera House.” Britannica. Britannica Kids, 2021.