SYDNEY (AFP) ― The Sydney Opera House, world heritage-listed as “one of the indisputable masterpieces of human creativity,” celebrated its 40th birthday Sunday with a flotilla of lifesavers, Aboriginal dancers and a gigantic cupcake.

Huge crowds packed the steps for a distinctively Australian performance on the glittering harborfront, where three generations of Danish architect Jorn Utzon’s family were the guests of honor.

It was a postcard-perfect day beneath the same cloudless blue skies that inspired Utzon’s winning design to build Sydney an opera house back in 1956 ― the white sails drawn from his childhood in the Aalborg shipyards.

“A building like this happens once in a lifetime,” Utzon’s son Jan told revellers on Sunday.

“It is a unique Australian expression of will and enthusiasm and ‘let’s go do it’ kind of spirit.”

The distinctive performance hall is one of Australia’s best-known landmarks and centerpiece of Sydney’s cultural scene, hosting some 2,000 shows every year and attracting 8.2 million visitors.

Utzon won an international design contest to build the harbor city an opera house in 1956 that attracted 233 entries from 28 countries, despite being relatively unknown in the architecture world.

His ambitious blueprint, drafted from photos and maps without ever having visited the harbor site, took 14 years and A$102 million ($98.66 million) to complete, funded by a state lottery.

It was one of the most difficult engineering feats ever attempted at the time, with Utzon envisaging a chamber with vaulted roofs unsupported by pillars or columns.

Custom-built French cranes were used to piece together the iconic sails segment by segment in mid-air, with pre-cast concrete ribs interlocking in an intricate jigsaw.

Some 1,056,006 individual tiles coat the exterior, custom-made from clay and stone. Utzon was inspired by Japanese ceramic bowls, imagining their pale matte finish would perfectly offset the blue of Sydney’s harbor and sky.

The Opera House was listed a world heritage site by UNESCO in 2007, the year before Utzon died.