This story is part of Women of Impact, a National Geographic project centered around women breaking barriers in their fields, changing their communities, and inspiring action. Join the conversation in our Facebook group.

Today, women are climbing to the top of the world’s highest peaks, diving into the ocean’s depths, and skiing across both poles, but it wasn't long ago that women were discouraged from taking on these formidable adventures.

Meet four remarkable pioneers who refused to be deterred by their gender and tackled some of the world's harshest landscapes—blazing a trail for the next generation of explorers.

Miriam O’Brien: Manless Climber

In the early 1930s, National Geographic editors learned of an adventurous young woman named Miriam O’Brien—thanks to a letter from her mom. O’Brien was pioneering what they thought of as a novel new sport: climbing mountains without men.

View Images Alice Damesme, Jessie Whitehead, and Miriam O’Brien pose for a photograph on the horses they'll ride to the Matterhorn hut. O'Brien and her climbing partners made the trip so many times they felt they'd become familiar with each of the animals who traveled the route. Photograph by , Nat Geo Image Collection

In August 1934, her story was published in National Geographic magazine, titled “Manless Alpine Climbing: The First Woman to Scale the Grépon, the Matterhorn, and Other Famous Peaks Without Masculine Support Relates Her Adventures.”

When her editor wrote that the first draft was too modest, she responded: “While at first glance it seemed easy enough to insert sentences and paragraphs saying, ‘I am an extraordinarily good climber, and altogether a remarkable woman’ in practice this turned out to be difficult to do gracefully.”

Meant as self-deprecation, the description was also accurate. Raised by a mountaineering mother, O’Brien spent her summers conquering the peaks of New Hampshire and, later, Europe in an era when female climbers were rare. She soon realized that following someone up a mountain wasn’t entirely satisfying.

“The one who goes up first on the rope has even more fun, as he solves the immediate problems of technique, tactics and strategy as they occur,” she wrote in her autobiography, Give Me the Hills. “I saw no reason, why women, ipso facto, should be incapable of leading a good climb… I decided to try some climbs not only guideless, but manless.”

“Now that it has been done by two women alone, no self-respecting man can undertake it,” a male climber complained after O’Brien and a friend led the first “manless” ascent of the Grépon in the French Alps in 1929. But there was no stopping O’Brien, who did the same on the Aiguille du Peigne peak and, in 1932, conquered the Matterhorn on the first women-led expedition of its kind.

Myrtle Simpson: Skiing Trailblazer

After one month and 375 miles of slugging across the frozen tundra of Greenland, Myrtle Simpson felt, as she later wrote, “some small pride to be a woman standing where no woman had stood before.” On that day in June 1965, the radiologist-turned-explorer had become the first woman to cross the ice cap.

Simpson’s husband, Hugh, was a pathologist studying whether the human body adapted to extreme and extended stress over time (he later concluded it did not). But in the article she wrote for National Geographic, Simpson was quick to point out that they would have attempted the feat of crossing Greenland by foot regardless—for the adventure alone.

The story, proposed to National Geographic, was a hit when editors realized what a feat had been quietly accomplished. “I should point out that, as far as we know, Mrs. Simpson was the first woman ever to trek across Greenland,” read one memo. Mountaineer Barry Bishop, who’d been part of the first American team to summit Everest three years prior, “thought this was a most extraordinary feat for a woman.”

At Hugh’s urging (“My wife writes a better version but I can’t admit this!!” he wrote to National Geographic), Myrtle was the one who authored the piece. The resulting story, titled “First Woman Across Greenland’s Ice,” paid proper dues to its pioneering writer, who had “climbed and explored from Australian outback to the Andes, from Spitsbergen to Surinam.”

View Images Ann Bancroft celebrates a successful expedition to the North Pole. Photograph by Jim Brandenburg, Nat Geo Image Collection

Ann Bancroft: Pole Pioneer

Ann Bancroft’s arrival to the South Pole in the middle of January 1993, made her the first woman to trek across both Poles. It took Bancroft and her three female expedition members 67 days to ski to the South Pole, each lugging 200 pounds of supplies. Two of them were nearly evacuated due to illness, but the group decided to slow down, stick together, and cross the finish line together. “We pulled our sleds, stood shoulder to shoulder, and had fun doing it,” Bancroft told National Geographic.

Seven years earlier, Bancroft, a Minnesota school teacher and mountaineer, had become the first woman to cross the North Pole. Her expedition made the journey by bobsled without additional supply drops for the first time since Robert Peary’s attempt in 1909. It was a brutal 55-day trip—food became scarce and Bancroft suffered a dangerous plunge through the ice into freezing water. When considering that she’d be the first woman to compete the feat, she wrote in her journal: “I truly never think of being the first female to the Pole. I’m basically so busy trying to get there.”

Her trailblazing visit to the poles wasn’t the last record Bancroft set—she also led the first American women’s team across Greenland and was the first woman, along with her travel partner, to ski across Antarctica. In 1995, she was inducted into the National Women’s Hall of Fame.

Gerlinde Kaltenbrunner: Queen of the 8,000-Meter Club

In 2011, Gerlinde Kaltenbrunner, an Austrian nurse, joined the prestigious club of mountaineers who’ve climbed all 14 of the world’s 8,000-meter (26,247 feet) mountains. She had carved her own way and earned a distinct title: the first woman to summit them without using supplementary oxygen. She also refused to use Sherpas or high-altitude porters—two more aids few climbers go without.

Her final peak was sharply angled K2, considered to be one of the world’s deadliest mountains. It was her fourth attempt, after one the previous year had ended in the death of her climbing partner. This time, Kaltenbrunner traveled with her husband and a small team. When he turned back at the sign of bad weather and urged her to join him, she refused. Days later, she reached the summit.

GERLINDE KALTENBRUNNER SHARES STORIES FROM K2 In 2011, mountaineer Gerlinde Kaltenbrunner became the first woman to summit all 14 of the world's 8,000-meter peaks without supplemental oxygen by completing a daring climb of K2.