Imagine the pressure of being tasked to securely hang a collection that includes a six-metre-long Brett Whiteley painting, or a nine-metre-long John Olsen or Tim Storrier. Now imagine being charged with commissioning new outdoor sculptures and soundscapes that can hold their own alongside these rock stars of the visual arts world.

That was loosely the job description given to Leon Paroissien when he was invited to curate a largely unseen and hugely valuable collection of artworks, reportedly valued at around $23 million. The NSW state government owned collection is now on display at the International Convention Centre (ICC) in Darling Harbour. Finished in 2016, the $1.5 billion ICC was part of a larger $3.5 billion revitalisation project for the precinct.

Paroissien, the founding director of the Museum of Contemporary Art and the chair of the City of Sydney Public Art Advisory Panel, seems to have carried out the task with aplomb.

There are now 30 local and international pieces within the collection, which has been referred to as “Sydney’s secret collection”. And for good reason.

Its collation began in 1988 during the first major redevelopment of Darling Harbour and Australia’s bicentennial celebrations, but it has been in storage since the site was demolished for rebuilding four years ago. Today the paintings are exhibited across the ICC’s main theatre foyer spaces and can be viewed by simply wandering through the vast structure.

The government already owned many of the works on display, such as the Olsen and Whiteley, but others were commissioned, with artists given a brief to create works relating to Sydney, its harbour and foreshore. Later, artworks were gifted or purchased to make the collection more complete, correcting the glaring omission of both female and indigenous artists.

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There are now major pieces from Lloyd Rees, Sandra Leveson and John Firth-Smith, in addition to key works from Gloria Tamerre Petyarre and Long Jack Phillipus Tjakamarra.

Like many others, Paroissien was astonished by the calibre of paintings. “I was amazed,” he says. “The value is astronomical … the nucleus of works you’d be very happy to see in any state galleries; they’re wonderful works.”

Paroissien’s role was to help restore, add to and curate the hanging of the existing collection in sympathy with the new site. “In the old [convention centre] the paintings were spread across the building, you came across them by accident,” he says.

Unlike curating an exhibition for an art gallery, Paroissien had to acknowledge the building’s use as a function centre – food and drink are often within spilling distance. The space also has expansive windows, so expert teams and machinery were brought in, including a professional conservator, to ensure the light streaming in won’t damage the canvasses (they are sheeted for filtering UV light).

Hanging the largest paintings, some of which reach three storeys high, was also tricky. “Some of them were very heavy and required special treatment and machinery to actually get them up [on the wall], and needed special backing so they could be hung almost to the specifications of a gallery,” Paroissien says. “To move them anywhere was a major operation … I joked with them about needing to move one slightly up or down.”

The result is impressive, particularly the main gallery in the heart of the building where the paintings are displayed in a semi-circle with a circular skylight bathing them in ever-changing light.

Unfortunately access is only open to those attending a show, convention or event, but if you don’t have a ticket, there’s still plenty of art to take in outside the ICC.

Although Paroissien didn’t commission additional works for the interior, he used the available $2 million budget for four new outdoor artworks, three of them from local artists.

Popular Japanese sound and digital artist Ryoji Ikeda’s 96-by four-metre digital artwork data.scape has become one of the most Instagrammed images in the precinct; while there are 12 sculptures by local artist Maria Fernanda Cardoso (eight of the sculptures are in for repairs, having been received a little too much love from enthusiastic skateboarders). Elsewhere a stunning concrete etching by indigenous artist Danie Mellor stretches seamlessly alongside the natural landscape.

Paroissien discovered Ikeda through his work at the Museum of Old and New Art (MONA) in Hobart. “I googled him and he wasn’t that well known, although he’d done Superposition at Carriageworks in 2015 [an immersive digital and live performance]. Since commissioning him, the popular artist has now become one of Japan’s leading electronic composers and visual artists. But data.scape is the only permanent installation of his work that exists,” Paroissien says proudly.

Mellor’s work Entelekheia evokes the native fauna that existed in the area in pre-colonial times, “when Aboriginal people were in harmony with the landscape”, and artist Janet Laurence’s piece is a soundscape of birdcalls from birdlife previously native to the area.

For her 12 sculptures, Sandstone Pollen, Cardoso created images of the pollen found on locally native and imported species. “Beautiful works,” Paroissien says.

The International Convention Centre’s art collection is open to those attending a show, convention or event. The outside art is available at all times. A self-guided tour map is available from the Convention Centre customer service desk.

For stories that relate to the ICC, see here. Or if you are interested in art, see this recent news story on Brett Whiteley.