The 4.2km (2.5 miles) tall figure, on a remote plateau in South Australia, is often thought to depict an Aboriginal hunter.
Dubbed Marree Man after a nearby town, it is one of the world's largest designs to be etched into the ground.
But mystery surrounds who created it - and why.
Earlier this week, Australian entrepreneur Dick Smith offered a $5,000 Australian dollar (£2,800; $3,700) reward for any information about the artwork's origins.
"How has it been kept secret for 20 years?" he said on the Australian Broadcasting Corporation (ABC) on Monday.
