On Friday, local time, William and Catherine trekked three hours to the holiest site in Bhutan, the Tiger's Nest monastery 3048m up in the Himalayas.
William quickly broke into a sweat, but Catherine stayed fresh.
Despite wearing a leather jerkin and calf-length leather boots for the arduous, rocky climb, she looked as though she had been for an easy stroll in the garden as she reached the site.
William, with beads of perspiration on his forehead, admitted the climb had been "quite tough" and his wife joked it was "a great way to burn off the curry".
The royal couple went one better than Prince Charles, who only got halfway to the monastery in 1998, not wanting to "risk" the full climb because he suffered from vertigo.
William said: "My father didn't make it to the top. So that's something I'll be reminding him of when I see him."
He also disclosed the couple have been phoning Prince George and Princess Charlotte regularly during their week-long tour of Asia and are missing their children "massively".
When they reached the halfway point of the climb after 45 minutes of steep trekking in the thin mountain air, the Duke was showing signs of the effort.
"So far, so good," he said, laughing, to the waiting media.
The 17th-century Taktsang Palphug Monastery, better known as the Tiger's Nest, is the cradle of Buddhism in Bhutan. It lies in the Paro valley, around 90 minutes' drive from the capital, Thimpu.
The King of Bhutan sent some of his own horses to accompany the Duke and Duchess in case either struggled, but neither needed the help. As they paused at another viewpoint nearer the top of the climb, the Duchess described the view as "very special ... it's amazing, so beautiful".
