Home » Latest » Outdoors » World-class sinkholes attract divers to South Australian farms

World-class sinkholes attract divers to South Australian farms

3

InfoSearched 61 0 Outdoors

5.8

SaveSavedRemoved 0

A working dairy farm south of Mount Gambier is hiding one of the deepest sinkholes ever surveyed in South Australia.

From the road, Trevor Ashby’s property looks like any other Limestone Coast dairy operation — cattle, fences, flat green paddocks. But beneath one unremarkable patch of grass sits a one-meter-wide hole that drops into a submerged cavern big enough to swallow a football field. Divers call it The Shaft, and it draws technical cave divers from across the globe to a spot most people would walk straight past.

• The Shaft’s underwater chamber spans roughly 140 meters by 80 meters and has been surveyed to depths beyond 120 meters, making it the deepest recorded sinkhole in the region.
• Ashby’s grandfather discovered it in 1938 when a horse punched its hoof through the paddock while plowing; the family later dumped an estimated 1,000 tonnes of rock down the hole trying, unsuccessfully, to fill it in.
• A 1973 diving accident that killed four people at the site led directly to the creation of the Cave Divers Association of Australia (CDAA), which now controls who is allowed to dive there.

A Cow Paddock With a Secret

Trevor Ashby is a third-generation dairy farmer, and for decades his family had no idea what was actually under their pasture. The discovery came by accident in 1938, when his grandfather was plowing the field and a horse’s hoof broke through the ground into open space below. Not understanding what they’d found, the family tried to make the problem disappear by tipping roughly 1,000 tonnes of rock down the opening.

It didn’t work. “We really didn’t have a clue how big it was underneath. We had no hope of filling it up,” Ashby said. What’s left of that effort now sits 35 meters down, a mound of rubble that Ashby compares to a submerged anthill — a visible reminder of just how badly the family misjudged the scale of what was beneath their cows.

The Scale Below the Surface

The surface opening is barely a meter wide, narrow enough that divers and their gear have to be winched down separately rather than climbing in together. Past that tight aperture, though, The Shaft opens dramatically into a chamber roughly 140 meters long and 80 meters wide, plunging past 120 meters in surveyed depth — the deepest recorded sinkhole in the region.

Cave diving instructor Gary Barclay has watched the reaction of visiting divers play out over and over. “We’ve had people who have dived all around the world and have come to here and they just couldn’t believe the size of the room that we’ve got under our feet here in the middle of a cow paddock,” he said. Around midday, sunlight beams straight down through the narrow entrance and lights up the crystalline water below, turning what’s normally a pitch-black void into something briefly visible from above.

“We’ve had people who have dived all around the world and have come to here and they just couldn’t believe the size of the room that we’ve got under our feet here in the middle of a cow paddock.”

A Tragedy That Built the Rules

The Shaft’s history isn’t only about scale — it’s also tied to one of the darker chapters in Australian cave diving. A 1973 accident at the site claimed four lives, a loss that became a turning point for the sport nationally and directly led to the formation of the Cave Divers Association of Australia (CDAA). That organization now sets the standard for who’s allowed underground in sinkholes like this one.

Access to The Shaft today is strictly controlled: divers need both landowner approval from Ashby and formal CDAA cave certification before they’re permitted anywhere near the entrance. It’s a far stricter setup than the open-water diving culture most visitors are used to, and it exists specifically because of what happened there in 1973.

More Sinkholes Next Door

The Shaft isn’t the only underground attraction hiding on Limestone Coast farmland. Nearby, farmer Graham Kilsby owns the well-known Kilsby Sinkhole, another flooded cavern that’s built a reputation among cave and technical divers well beyond South Australia. Together, sites like these have turned an otherwise ordinary stretch of dairy and grazing country into a destination that regularly pulls in divers who’ve trained on formations all over the world — a phenomenon not unlike Australia’s other strange landscape quirks that keep surprising outsiders.

None of it changes what happens on the surface. Ashby still runs cattle over the same paddock where his grandfather’s horse found the hole in 1938, and getting into The Shaft still means clearing the same two hurdles it always has — his sign-off, and a CDAA card in your pocket.