It was an adventure into the unknown. From the surface all that could be seen was a small opening. Researchers had no idea how deep the hole went, or what was at the bottom.
The ABC has been given exclusive access to newly-discovered caves on South Australia's Kangaroo Island.
Kangaroo Island, which sits adjacent to South Australia's Fleurieu coastline, is a place of raw, natural beauty.
Its dense scrub, rugged coastline and unique flora and fauna attract visitors from around the world.
But in December 2019, the thick vegetation fuelled a bushfire crisis on the island.
Loading...What started as a small fire caused by lightning strikes, became a raging inferno.
It burned through more than 200,000 hectares of land, almost half of the island, and killed two people.
Almost 90 homes were destroyed as well as crucial habitat for countless native animals.
Thousands of livestock also perished.
But underneath the ashes, a hidden gem was waiting to be discovered.
With the thick vegetation razed, researchers used aerial imagery to pinpoint areas for exploration.
They knew there was high potential for ancient cave discoveries based on the island's geological history.
"It was a very difficult time for the residents of KI. There was a lot of struggle going on," cave researcher Andrew Stempel says.
"From the aerial surveys you could literally spot what looks like a depression.
"So, you send a team out, we walk through, and we go and literally stick our noses in every single hole and document everything.
"Once people sort of slightly healed, we discovered that there was an opportunity … to find these beautiful spaces that probably would have gone unnoticed to humanity."
The community of cave explorers is a close-knit and enthusiastic one.
People from across Australia travel to far flung locations in search of hidden treasure.
Matt Smith grew up scouting and has been caving since the age of 15.
He says the underground is one of the last frontiers for exploration.
"People see it as … 'surely the world's been very strongly documented' and I think that's the case for a lot of it, but the underground certainly offers a really wide range of unknown locations, similar to the ocean as well," Mr Smith says.
In October 2020, he and his group of cave explorers, made their first visit to Kangaroo Island.
They visited multiple sites, but it wasn't until their second trip in March 2021, that they made their most stunning discovery.
The opening to the cave was small and unimpressive.
"We didn't have high hopes," Mr Smith recalls.
They scaled down an eight-metre drop into the cave…
… discovering a space filled with beautiful and delicate limestone features, with tunnels which extended hundreds of metres.
Mr Smith and his colleagues initially named the cave "OMG", a moniker he says is commonly given to sites where they have "found something cool".
Loading..."It was certainly the best discovery we'd seen on our trips so far, and to this day remains the most extensive cave we've discovered as part of this research," he says.
"To be given these opportunities to actually kind of look in these caves and see them for the first time is a massive privilege for us," he says.
The cave was later called Phoenix…
… the nod to the mythological bird was an obvious choice.
"It got named Phoenix because it rose out of the ashes," caver Andrew Stempel says.
It has remained untouched for millennia, with researchers estimating the caves are between one and two million years old.
They say shell fragments from the exposed seabed deposited on the island's south and west coast.
The dunes then hardened over time, before rainwater dissolved the soft limestone to form the magical underground chambers.
Loading...The discovery of the Phoenix cave is one of many wondrous finds, and by the time researchers had finished surveying, more than 150 new caves had been found.
There had been 130 known caves before the fires.
"It's like one of the greatest experiences ever," Andrew Stempel says.
"So you know that mind-blown emoji? That's pretty much what happened."
Andrew Stempel, who is the president of the Australian Speleological Federation, grew up in the US and moved to Adelaide in 2014.
He swapped mountaineering for speleology, which is the scientific study of caves and their formation, structure, history and ecology.
"I moved here and there were no mountains, so I found a different passion, which was underground mountaineering and that's how I ended up here," he says.
He's currently doing a PhD in ecology and evolutionary biology at Adelaide University, under the supervision of Dr Jess Marsh.
While the ABC films, they find what they believe is a previously undocumented spider.
It is now under DNA testing to verify whether it is a new species.
The discovery follows others made in the caves, including a tiny white spider which has no eyes, a newly-identified species which has physically evolved to live underground.
"We found some animals that have lived so long in the dark that they've become adapted to a cave way of life," Dr Marsh says.
"They've lost their eyes, they've lost their pigment, they're white. This is really exciting because those animals are exceptionally rare."
"So with insects and invertebrates and spiders, we're really just scraping the tip of the iceberg in terms of what's known out there," she says.
"With the animals that I've been finding in the caves, my records of them, for most of them, is the only record that's known.
"So prior to that, no-one knew about them … they were undocumented.
"By finding them, we can protect them."
It's clear that the cavers love their work.
But those uncomfortable in tight spaces or those who don't like getting dirty need not apply.
"I mean, not everyone likes to be covered in dust and dirt and I say to people, 'hey, it's a free mud pack, you know', but yeah, it's not for everyone," Flinders University adjunct lecturer in history and archaeology Clare Buswell says.
The hunt for the new caves, and re-identification of previously known caves, was made possible by more than $80,000 in grant funding from the South Australian government and the Australian Speleological Federation.
Dr Buswell is the project lead.
Dr Buswell says the caves reveal a lot about past climate conditions.
"So you know how if you cut a tree, it has rings in it and that rings tell you the growth of that tree and how it grew and whether it was a dry period or whether it was a wet period of growth," Dr Buswell explains.
"Stalactites and stalagmites tell you the same."
She says if you cut one of the "stals" in half, as they're colloquially called among the caving community, you'll see rings.
"Those rings and the distance between the rings will tell you whether it was a dry period of growth or a wet period of growth," she says.
"But more importantly, what we've been able to do just very recently is find how those growth rings relate to rainfall."
The newly-discovered caves are not open to the public and some of the researchers want to keep it that way.
But tourists can have their own underground experience at Kangaroo Island's Kelly Hill caves, which have been a tourist attraction for a century.
"To be thinking about all of this mapping and exploration of these new cave openings that are occurring and we're finding now, to think back 100 years ago, they were first going into the [Kelly Hill] cave," National Parks tour guide Gemma Carlsen says.
"Now they have a helmet and a head torch, whereas they had to do it by candlelight."
Ms Carlsen says the caves attract a diverse range of visitors.
"You get people that have never been in caves before. You get people that have been into hundreds of caves and watching their reactions to the cave is always incredible," she says.
"You get young kids come through that are a little reserved, a little scared, they don't know what to expect.
"It's their first time underground and they go into the cave and their faces light up with wonder."
Just as the Phoenix regenerates from the ashes, so too is the island.
It has been almost six years since the devastating fires, and many of the cave sites are yet again in hiding underneath regrown vegetation.
"There was a lot of loss in the bushfire. A lot of positives come from it as well… all these new cave openings," tour guide Gemma Carlsen says.
"For me personally, I see the recovery.
"I see the new life coming through, the little baby kangaroos, our echidnas coming through.
"The parks, the landscape, it is bouncing back."
Reporting: Angelique Donnellan
Photography: Che Chorley
Video: Carl Saville
Digital production and editing: Sara Garcia and Jessica Haynes
Top Phoenix images supplied: Allan Pryke
Fire images: Trent Lawson, Sabrina Davis & Trent Murphy
Fire video: Mark Harte
Video production: Julia Farrington