FIVE years ago, David Graham started to dig up his backyard, but what he found continues to baffle the Coverty man and his family to this day.
What started out as small rocks protruding from the ground have become deep, pool-like formations on the property.
"I actually came up here and thought people had been cementing rocks together into these pixie rings and I didn't know what it was until we started digging," Mr Graham said.
After four years of digging, with the help of his family, Mr Graham uncovered many mystery holes that cover at least four acres of his property.
The family has even got their hands on an air compressor and industrial vacuum to clear it out.
"We started to dig out of curiosity and once you start, you just want to see the end," Mr Graham said.
"I just want to know, what forces of nature were used to create these mystery holes."
Everything from an inland sea and volcanic activity to aliens and leprechauns with a bag of cement are among the theories Mr Graham and his family have entertained.
After studying photos of the formations, University of Queensland's Associate Professor for the School of Earth Sciences, Gideon Rosenbaum, said he believed the rocks were a result of chemical surface weathering.
"My guess is that the rocks were originally granites but the feldspar minerals were replaced by clays," Prof Rosenbaum said.
"It takes 100,000 years to create a one metre depth of the weathering profile, or 0.5 to one million years if the depth is five to 10 metres."
Mr Graham hoped to turn the holes into a local attraction, creating mini spas and a viewing bridge for visitors.
But he said this might be some time away.
"I dream about them bloody holes sometimes," he said.
"You don't expect too much off the land here but this is something else, it's something special and it needs to be seen.
"I just want the people of the South Burnett to know they've got something special in their backyard."
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