Harry climbed the iconic landmark in Australia Friday afternoon along with Prime Minister Scott Morrison. Not for nothing but it seemed Harry was nervous ... looking serious and holding on tight. Probs thankful the Mrs., Meghan Markle, stayed behind. She's got a good reason, with the pregnancy and all.

In case you're wondering ... the climb's nearly 500 feet and 1,332 steps. That's a lot of calories burned. He was up there to hoist the flag of the Invictus Games on the eve of the international Paralympic event ... founded by Harry.