Trevor Ashby's property south of Mount Gambier looks like a typical dairy farm from the roadside, but hidden among the cows is a tiny portal into a world-class dive site.

The hole in the ground is so small that equipment and divers have to be lowered in separately.

But below the humble entrance is a huge, seemingly bottomless chamber.

"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," cave diving instructor Gary Barclay said.

The Shaft, as it is known, is the darkest and deepest recorded sinkhole in the region, dropping more than 120 metres.

It was discovered by the owner's grandfather when he was ploughing a paddock and the horse put its hoof through the surface.

A pile of rubble 35 metres down was the family's unsuccessful attempt to fill it.

"We really didn't have a clue how big it was underneath. We had no hope of filling it up," Mr Ashby, a third generation farmer, said.

"It looks like an ant hill down there and we've tipped a thousand tonnes of stone down there."

Read the full story by Kerry Staight: https://www.abc.net.au/news/2015-06-1...

More Wild Rides on iView: https://iview.abc.net.au/show/wild-rides

Join the ABC Australia community on social media!

http://abc.net.au/
Facebook:   / abc  
Twitter:   / abcaustralia  
Instagram:   / abcaustralia