Mount Gambier in South Australia is home to 30 popular cave diving sites, but there are two extraordinary sinkholes that have gained international fame.
Lying beneath seemingly generic farmland, The Shaft requires expert divers to be lowered through a small manhole in the ground from a metal tripod. Inside, there's an eight metre free hanging drop to the surface of the water, where the cave's diameter is approximately 20 metres. The cave is about 120 metres deep, pitch dark and often described to be like outer space. Scientists often explore its depths to study the marine life and geology.
Kilsby's sinkhole (pictured), more visible than The Shaft and approximately 50 minutes away by car, is a limestone cavity that descends to depths of 65 metres. Well-known for its clear waters and unearthly landscapes, it has in the past been used by the government for weapons testing and police force deep dive training.