When British adventurer Bear Grylls started taking A-list celebrities on journeys into wildest locations around the world, he knew it was going to make great viewing.

It began during his Man vs Wild days, when he took Hollywood funnyman Will Ferrell on an Arctic adventure in 2009 to stalk bears and slide down sheer snow-covered cliff faces.

It continued over the years in single episodes with actors including Jake Gyllenhaal, Zac Efron and Brie Larson, as well as English model Cara Delavingne and Spice Girl Mel B.

He’s even taken former US President Barack Obama – plus 60 Secret Service officers and a few snipers in nearby mountains – on an extreme overnight outdoor adventure in the Alaskan Mountains.

Now, Grylls has a new pack of celebrities to put through their paces in National Geographic’s Running Wild With Bear Grylls: The Challenge.

“The celebrities will push their bodies and minds to the limit to successfully complete life-changing adventures that will challenge their perceived limitations,” reads the show’s synopsis.

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Natalie Portman, 41, an Oscar-winner and freshly-minted superhero in Thor: Love and Thunder, is the first guest to appear in the latest iteration of his long-running series.

In one scene during their 48-hour journey, she and Grylls need to find some fresh water. Fast.

No luck? Grylls expertly cuts away his Calvin Klein undies from beneath his waterproof pants, stretches the fabric over an empty flask, and gets Portman to pour filthy, muddy water scooped out a mountain crevice into it.

“We could use a sock, but then again, you kinda need your sock,” he says.

“We’re gonna filter sludge water through underpants?” asks the actress.

“I mean it’s not going to be perfectly clean,” Grylls admits, to which Portman replies: “That’s an understatement.”

“This is … gross,” she says.

But Grylls is happy: “Look at that! … Perfect.”

Onwards and upwards!

This season’s guests and locales also include another Marvel hero, Simu Lui, in the Canadian Rockies, Ashton Kutcher in the jungles of Costa Rica, yet another Marvel star, Florence Pugh, in the volcanic rainforests of Costa Rica, actor and comedian Anthony Anderson in the Sierra Nevada Mountains and soldier-turned-movie star Rob Riggle in the Great Basin Desert.

The attraction of dangerous treks

Bear Grylls was once asked why celebrities wanted to go along with his extreme survival treks.

He admitted to ecotourism travel website, Green Global Travel, they weren’t doing it for the money, the fame, or the exposure.

“These guys have all of that. They don’t need to take risks. And the truth of doing this is that it is a risk. You’re going to look like you’re not brave or strong.

“I think it’s a testament to the idea that people at heart love to challenge themselves.

“These guys have all reached top of their profession … all of these guys said one of the best bits was having space and time to think about life and how lucky they’ve been.

“The outdoors does that. It creates bonds between people and it gives us space to breathe. At the end of it, all of them had a smile on their face and a light in their eyes that money can’t buy.

“Fame doesn’t do it. Drugs don’t do it. Booze doesn’t do it. It’s the power of the wild, and I’ve seen it a tonne in people,” he said.

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‘Lucky to be alive’

Kutcher joins in the fun in Costa Rica in episode three, where he confides in Grylls his year-long battle with a “super rare” auto-immune disease.

Kutcher, 44, married to actress Mila Kunis since 2015, revealed he was “lucky to be alive” after he was diagnosed with a rare form of vasculitis nearly two years ago.

“Two years ago I had a weird, super-rare form of vasculitis that knocked out my vision, knocked out my hearing and knocked out all my equilibrium,” Kutcher said.

Vasculitis is an autoimmune disease that results in the inflammation of the blood vessels and restricted blood flow. There are many types of the disease, although Kutcher did not disclose the specifics of his diagnosis.

“It took me like a year to build it all back up again,” the That ’70s Show star said.

“You don’t really appreciate it until it’s gone until you go, ‘I don’t know if I’m ever going to be able to see again; I don’t know if I’m ever going to be able to hear again; I don’t know if I’m ever going to be able to walk again’.”

Kutcher, who has since fully recovered, added that he was “lucky to be alive” and spoke of his personal growth since his health scare.

“The minute you start seeing your obstacles as things that are made for you to give you what you need, then life starts to get fun,” he said.

“You start surfing on top of your problems instead of living underneath them.”

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Nominated for an Oscar for Little Women, Pugh travels to the volcanic Rainforests of Costa Rica in episode four.

Canadian actor, author and stuntman Liu, known for portraying Shang-Chi in the 2021 Marvel film Shang-Chi and the Legend of the Ten Rings, shouldn’t have any trouble in episode two in the Canadian Rockies.

Anderson goes off in the Sierra Nevada Mountains.

Former US marine and Holey Moley and 12 Strong actor Riggle brings it home in episode six in the Great Basin Desert between Sierra Nevada and the Wasatch Range.

Running Wild With Bear Grylls: The Challenge set to premiere locally on Foxtel and Disney+ soon.