An exhibition and concert taking place in Auckland's Silo Park are bringing life - and a soundtrack - to hidden lava caves lying under Auckland's central suburbs.
For those who know about them, the caves can be found below streets, beneath front yards and under rows of shops. They've been formed over the past 150,000 years by various eruptions of the city's volcanoes.
When the eruption stops and the stream of lava begins to cool, the lava pours out the end of a lava tube, hollowing out a cave under the ground.
Chirag Jindal, digital artist and architecture and planning graduate, worked with speleologist Peter Crossley to capture the network of caves in a series of 3D scans, created using surveying equipment.
In Jindal's words, the images are formed by "millions and millions of little points", gathered through a high-tech LiDAR scanner.
"The LiDAR scanner works by laser - it's basically a 3D scanning device. It captures the world around it and makes a digital replica using laser," he said.
"In the images you see these little bright clusters. That's where the scanner was placed, so we went to the other side of the cave and essentially moved it through the cave on the surface, letting it connect the scans together."
The images were currently on display at Wynyard Quarter's Silo 6 for the Festival of Architecture.
Tonight, musician and award-winning composer Peter Hobbs will play live at the exhibition - a performance he was hoping would "capture the essence" of the environment inside the caves.
Hobbs, a multi-instrumental improviser, would be joined by Charmian Keay on violin, cellist Maxine Cunliffe and pianist Brendon Morrow for the performance.
The musical quad had already performed the musical score inside one of the caves.
While Hobbs said it was an experience, he also said he hadn't foreseen how much of a "nightmare" it would be to lug their musical instruments to the spot.
The musicians had to carry their gear over rocky terrain into the cave to set up shop while concert-goers scrambled over boulders to get there - a far cry from the steps of the Town Hall.
Based on Crowley's research, there were at least 50 caves with about 250 entrances.
Jindal pointed out hundreds more could exist in the Auckland region, but no one would ever know until they started digging.
Private developers often wouldn't report caves if they found them, he said, as public knowledge of the natural feature could undermine their plans for the land.
"They're completely disregarded for what they are," he said.
"It's remarkable how they've ended up in a relationship with the natural environment."
The usual reaction of residents when discovering a cave sat underneath their home, was "holy sh**", Jindal said, followed by some degree of awe.
"At the end of this there's some level of stewardship, of recognition that these caves are part of our history."
Hobbs approached Jindal several days before he opened a similar exhibition in December last year, and wound up performing an improvisation on the night.
This year, leading up to the second exhibition, Jindal said they wanted to turn the musical element of the exhibition up a notch.
"The idea was to refine it further," he said.
"We wanted to capture the essence of the sites, by performing the music inside the caves."
So last month Hobbs and his small crew of musicians held a recording session in a cave deep below the dormant volcano Te Tātua-a-Riukiuta, in Three Kings, and invited people to come along.
The group approached local Iwi for permission to perform inside the caves - as several had been used as burial caves.
The recording was playing in Silo 6 over the course of the exhibition, bar tonight, when the live concert was taking place.