Daring divers have discovered the second-largest known cave on South Australia's Limestone Coast after three years of exploration.
The world famous Engelbrecht Cave system, situated in a residential area in Mount Gambier, runs beneath highways, houses, businesses and schools.
It extends about 300 metres to the west and, previously, 70m to the east — but the eastern section now spans about 400m, thanks to the curiosity of Josh Richards and his diving companion, Matthew Aisbett.
In 2019 the two men were tipped off about a potential subterranean passage.
"We were told by another diver that there was a bit of water at the end of this rock chamber in Engelbrecht Cave," Mr Richards said.
"While we were swimming around, they shone a light up towards the roof and saw a reflection.
"We popped our heads up and the reflection turned out to be a surface lake that led to more dry caves and we thought that was very interesting.
"It wasn't on any of the maps, so we doubted anybody knew about it."
'Like a spider web'
The team's breakthrough discovery came in mid-2021, when Mr Richards noticed a stream of silt travelling in an odd direction.
"I swam down into the pool to see where the silt had gone and all of a sudden I was looking down into this gaping tunnel that we've never seen before," he said.
"It kept going and it went vertical into a chimney, when we got to the top it opened up into this enormous room that would be twice the size of the ABC studio in Mount Gambier.
"That was very overwhelming.
"To think this cave that people had been diving and exploring for the last 50 years had this little tunnel at the back that opened up into this enormous cave network — we were mainly in shock the first time we found it."
Mr Richards said the passage was about 400m long.
"If we do find a connection to the Cave Gardens, that will be 1.4 kilometres of passage in a straight line," Mr Richards said.
"There's little doubt there are branches that spring off, like a spider web, right across Mount Gambier — we just haven't found them yet."
Into the 'Rabbit Hole'
A tight restriction in the cave system had to be navigated by Mr Richards and his diving companions to discover what lay beyond.
"The one restriction has stopped exploration in the past and it has the potential to be quite dangerous," he said.
"One of my great friends actually got stuck there a few months ago.
"I had to hold his head up so he wouldn't drown in 20 centimetres of water."
Mr Richards conceded there had been some close calls.
"But we've learned a lot and put in rules around how people navigate getting through that piece of rock which we call the Rabbit Hole," he said.
Ryan Kaczkowski has been diving in the Mount Gambier area for 20 years and says such discoveries are rare in "the diving capital of Australia".
"This is where everyone comes to do their training and because people have been diving here for so long, there is a lot of easy access to train in," Mr Kaczkowski said.
"New discoveries around here mean you are using the newest and best techniques and fresh eyes to notice what no-one has before."
"That's why a discovery like Josh's is so amazing."
Subterranean romance
Mr Richards was short-listed for the Mars One project but changed his focus after the enterprise was scuppered.
"Rather than spend so much time looking at the stars, I wanted to find out what was going on under Mount Gambier," he said.
Mr Richards said the support from fellow diver Chloe Reid had been instrumental throughout the exploration.
"It's a sport that I find quite calming and relaxing, but it's still challenging and exciting," Ms Reid said.
"These dives supporting Josh on finding and pushing the Engelbrecht extension have been absolutely mind-blowing.
"It really is hard to describe just how exciting it is to find yourself in a part of the cave that next to nobody has ever been in before."
In one such newly discovered cave, Mr Richards made a "cheeky proposal" to Ms Reid.
The two are expecting to share many adventures in the future.
