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.

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.

In August 1934, her story was published in National Geographic magazine, titled “Manless Alpine Climbing: The First Woman to Scale