Umpherston Sinkhole, Mount Gambier

Umpherston Sinkhole is a collapsed limestone cave in Mount Gambier, South Australia, transformed into a spectacular sunken garden with terraced garden beds, exotic ferns, palms and a century-old Moreton Bay fig tree at its base. The sinkhole is approximately 50 metres wide and 20 metres deep, with viewing platforms and a series of steps descending into the garden. At dusk, thousands of possums emerge from the surrounding gardens and climb the trees — a nightly spectacle that draws visitors. The surrounding Umpherston Reserve also contains a second, less developed sinkhole. The cave formations are estimated to be over 30 million years old.