With wife Kate watching (and a protection officer with a safety harness standing next to her), William, 31, caused some nervous gasps when he stepped up to the edge of the cliff while visiting the Blue Mountains west of Sydney.
The royal couple were visiting Narrow Neck Lookout and observing young people abseil down the cliff while on an adventure training course.
Showing no fear, William stood just 18 inches from the edge. "He took a bit of a lunge, and a few people held their breath, gasped and readied their hands to grab him," Damian Cooper, manager of the Mountain Youth Services Team, told reporters.
"I think he made everyone a bit nervous. He took a step over and took a look down. I had a brief moment there. He did not seem intimidated by the edge or the height at all. He was fine."
Tim Williams of the Blue Mountains Adventure Company added: "He was calm on the edge. He didn't worry about the safety briefing to stay a distance back. He just stepped up to have a cool look over. It's just his military training, I guess."
The couple also visited the Blue Mountains' most famous beauty spot – the Three Sisters rock formation. They walked slowly past a crowd of thousands of well wishers, some of whom had driven hundreds of miles to catch a glimpse of them.
Posing for a portrait at the stunning spot, they gazed out at the three rocky outcropping, which legend says were once three sisters who were turned to stone when they fell in love with men from another Aboriginal tribe.
Three members of local Aboriginal associations gave William and Kate two furs – one made of possum skin for George, and one of local kangaroo fur for them. "That's fantastic. Thank you very much. He'll love that," William said.