It’s opening night at Capitol Theatre. As I listen to the speeches, and while the gold ribbon is being cut to the sound of the Indiana Jones theme, it’s hard not to look up at the ceiling, jagged and ornate. It’s like an elevated version of Superman’s Fortress of Solitude. RMIT Pro Vice-Chancellor Paul Gough isn’t exaggerating when he calls it “one of the most astounding cultural artefacts in the world.”

It’s a beautiful theatre and an asset to the city. 580 comfy seats, state-of-the-art audio and two projection booths with 35mm film and 4K digital capabilities. But the real marvel is the architecture. Designed by American architects Walter Burley Griffin and Marion Mahony Griffin, who also designed the city of Canberra (this is nicer), it’s a marvel.

It’s both exciting to see the old cinema given new life, and infuriating that it’s been hidden in plain sight on Swanston Street for so long.

“Think of the amazing buildings and their ceilings in this stretch, from the NGV Great Hall to the dome of the State Library,” says Professor Lisa French from the School of Media and Communication. “And this is a dead spot in the city, right opposite the Town Hall? That’s completely mad.”

The Capitol closed five years ago, and over the last two a team from RMIT have been working to restore it, opening up spaces that have been boarded up since before it closed. By day, it’ll be a lecture theatre and learning space. Architecture students will study it. Film students will see their work on its screen. Event management and hospitality students will use the function spaces.

Then, by night, it’ll be a cinema, like it was always destined to be. MIFF, the Melbourne Queer Film Festival and the Japanese Film Festival are screening at the Capitol this year, and it’ll be used by ACMI while its Fed Square cinemas are closed for refurbishment.

The building has a rollercoaster of a history. When it opened in 1924, screening Cecil B DeMille’s The Ten Commandments, it was a cutting-edge 2000-seat theatre acclaimed by architects and loved by patrons.

But 40 years later its capacity was reduced to 500 seats, and the architectural gem was under threat of demolition. Iconic Australian architect Robin Boyd described it as “the best cinema that was ever built or is ever likely to be built,” leading the charge for the building’s reprieve.

RMIT took over in ’99, using it as a lecture theatre and for the odd MIFF screening, but since 2014 it’s been, to quote chancellor Gough again, “mothballed”.

“Something needed to be done,” says Martyn Hook, dean of RMIT’s School of Architecture and Urban Design.

The Capitol is a landmark for many reasons. It was a major commission for two celebrated American architects in a city used to stuffy English design. And it was a key work for Mary Mahony, one of the first women in the world to become a licensed architect (though for years her husband Walter got sole credit). As with the pair’s Canberra design, the drawings were all hers.

“She was the talent,” says Peter Malatt, director of Six Degrees Architects. “He was the salesman.”

Malatt worked on the Capitol’s refurbishment when RMIT took it over in 1999. He remembers coming here as a kid, but his fondest memory of the place is re-lighting that ceiling for the first time. “There was a sharp intake of breath,” he remembers. Now, again fully restored and re-lit, the elaborate ceiling is made from solid-cast plaster hanging from an intricate timber frame.

There’ll be a few more sharp intakes of breath when Melburnians see what they’ve been missing out on. The first public screenings kick off on Wednesday June 12 with a double bill from mid-century German filmmaker Max Ophüls, followed by a season of films by French New Wave auteur Agnès Varda, which is presented by ACMI.