Today’s explorers have to go to great lengths to uncover anything genuinely new. The deepest corners of the ocean and the farthest reaches of space are two of the last true frontiers. That’s because a generation of remarkable people led us to map and explore almost every inch of the Earth.

Naming the people responsible is often a challenge, however. We sometimes forget what an accomplishment it is to visit a place completely unknown and foreign to us. In acknowledgment of that incredible courage, here’s our list of the top 12 most influential explorers of the 20th century.

Sir Edmund Hillary and Tenzing Norgay — New Zealand and Nepal

In the modern age, anyone with enough money and decent physical training can summit Mt. Everest. But when Hillary and Norgay did it in 1953, only about 12 attempts to reach the top had been made, with 13 fatalities. Hillary and Norgay proved after 6 attempts that the tallest mountain in the world was possible to climb, and Norgay created a legacy for the Nepalese Sherpas who would follow in his footsteps.

Amelia Earhart — USA

A pioneer of flight and an icon for women, Earhart is too often remembered for the strange nature of her demise. Her trans-Atlantic solo flight in 1928 and trans-Pacific flight in 1935 represent the second and first crossings of these oceans by any person, opening the door for commercial air travel.

Jacque Cousteau — France

The ocean’s depths are still some of our planets least understood places, but when Cousteau began his work in the 1930s, none of the equipment we have today existed. His work led to the introduction of modern SCUBA equipment, he discovered the patterns of echolocation used by whales and sea mammals and brought he vastness of the ocean into our living rooms with his series, “The Undersea World of Jacques Cousteau.”

Percy Fawcett — UK

During the early 20th century, the African interior still presented a profound mystery to the world. Percy Fawcett and his son vanished into the Amazonian rainforest in 1925 in search of the mythical city of El Dorado, or as he called it, “the Lost City of Z.” It capped off the last great age of British exploration.

George Mallory — U.K.

More than twenty years before Hillary and Norgay, renowned adventurer George Mallory lead a pioneering expedition to the Everest region. He ascended nearly the entirety of the deadly climb before turning back. A later attempt to summit Everest in 1921 would prove fatal for Mallory. But his legend was already well-established thanks to numerous other mountaineering expeditions in the early 20th century.

Roald Amundsen — Norway

Perhaps less glorified than the peaks of Nepal, the world’s poles are equally unforgiving. The Norwegian Amundsen leveraged exceptional sailing skills to navigate some of the world’s most challenging seas, threading the infamous Northwest Passage to visit the far reaches of Alaska and later the North Pole in 1909. Two years later he reached the South Pole, the first to do so.

Dean Potter — USA

We remember some explorers for advancing their craft as well as our knowledge of the planet. Dean Potter is one of the most recognizable names in climbing thanks to his pioneering contributions to the art of free-soloing, a feat he was the first to attempt at-large. He plotted numerous routes, including famous climbs in Yosemite that continue to make news today thanks to people like Alex Honnold, who followed in Potter’s footsteps. Potter also made contributions to the sport of wingsuit flying, which sadly led to his untimely death.

Chuck Yeager — USA

Exploring the boundaries of speed and flight, the test pilots of the 1950s were truly exposing themselves to impossible-to-predict conditions. Already a decorated WWII pilot, Yeager was the first person to travel faster than the speed of sound, going on to break Mach 2 as he traveled at 1,650 miles per hour in his X1 test plane. That can’t have been a smooth ride, but it did advance aviation technology in ways few other pilots have.

Sir Ernest Shackleton — UK

While Shackleton lost the race to the South Pole to Roald Amundsen, his expedition didn’t stop when he got there. Instead, his team famously pressed on until they trapped their ship in ice. Shackleton’s great feat was one of survival. He brought all 28 men on his expedition back alive after two years of life on arctic ice flows, one of the greatest survival tales of the 20th century.

Buzz Aldrin and Neal Armstrong — USA

Last on our list and perhaps the best known of all are the two American astronauts who set foot on the moon. Of all the remarkable feats accomplished by those on this list, space exploration is perhaps the most audacious and far-reaching. Technology developed from the space program has trickled down into modern electronics, and we’re still learning more about the way we can benefit from researching the expanse of space today.

A Leap Into the Unknown

There will always be those who seek to explore and push the limits of what the word exploration means. That might be harder to grasp in 2020 than it was for these men, but perhaps it’s only a lack of imagination that keeps us from taking that leap into the unknown. Nothing about any of what these ten accomplished would have been considered “normal” by the standards of their times, but as we can see, that didn’t hold them back.