History is full of intrepid individuals who went out on a journey, never to return. From a record-breaking mountain climber to a British adventurer who may have died searching for a city that doesn’t exist and beyond, these explorers have fates that are shrouded in mystery.

1. Amelia Earhart

Amelia Earhart and her navigator, Fred Noonan, seemingly vanished on July 2, 1937, during Earhart’s second attempt to become the first pilot to circumnavigate the globe around the equatorial region. The fact that neither their bodies nor their aircraft were ever recovered is common knowledge, but one theory regarding their fate isn’t as well known.

According to the International Group for Historic Aircraft Recovery, it’s possible the duo got lost and landed on Nikumaroro Island in the Pacific Ocean. This would explain the human bones and U.S.-made artifacts found on the remote island in the years following their disappearance. It would also explain why complete remains of the pair were never recovered. Nikumaroro is crawling with coconut crabs, which grow to be up to 3 feet across. They’re known to eat pretty much anything, including the remains of large mammals. In one study involving a pig carcass, coconut crabs dispersed the animal’s bones as far as 60 feet from their original location.

The coconut crab hypothesis is just one of many theories surrounding what happened to the trailblazing aviator, but it may be the creepiest.

2. and 3. Gaspar and Miguel Corte-Real

In 1500, Gaspar Corte-Real became one of Portugal’s most accomplished explorers. That year, he led an expedition to Greenland. Sure, he thought the icy shores belonged to East Asia at the time, but it was an impressive journey nonetheless. He made a return trip to the region in 1501, and this time he brought along his older brother Miguel. After going to Greenland and then hitting what may have been Newfoundland, two of the fleet’s three ships returned to Portugal, including the one captained by Miguel. Gaspar’s vessel, however, never made it home.

When Miguel Corte-Real learned that his brother was missing, he organized a rescue mission to find him. They searched the area where he was thought to have ended up, but there was no sign of the lost explorer. Once again, all but one of the fleet’s ships returned to Portugal, and this time it was Miguel’s ship that never made it back to port.

A third brother—Vasco Anes Corte-Real—was willing to launch a second search party to recover his lost siblings, but the king of Portugal denied his request. Based on the family’s track record, it was probably for the best.

4. and 5. Vandino and Ugolino Vivaldi

The Corte-Reals weren’t the only well-traveled siblings who disappeared in their travels. In 1291, Genoese brothers Vandino and Ugolino Vivaldi became some of the first European explorers to set sail in search of passage to Asia. After entering the Mediterranean Sea through the Strait of Gibraltar, their expedition was never seen again.

Though technically a failure, the Vivaldi brothers’ doomed journey wasn’t for nothing. The mistakes they made helped lay the foundation for more successful voyages down the road. By the time Christopher Columbus sailed the ocean blue in 1492, he knew which type of ship was best for the job and how to use wind patterns to his advantage—insights the Vivaldis weren’t lucky enough to have in the 13th century.

6. Naomi Uemura

At this point, it can seem like we’ve mapped every corner of the Earth, but that hasn’t stopped modern explorers from going missing. In 1984, 43-year-old Japanese adventurer Naomi Uemura vanished while climbing Alaska’s Denali—formerly known as Mount McKinley.

Uemura was hardly an amateur explorer. A thrill-seeker from a young age, he was part of the first Japanese expedition to summit Mount Everest in 1970. He also completed the first solo expedition to the North Pole and the first solo raft trip down the Amazon River. He had also successfully climbed to the top of Denali in 1970, making him the first person to do so unaccompanied. Fourteen years later, he attempted another first: climbing the mountain’s peak alone in winter.

Despite the perils of climbing in Alaska that time of year, Uemura accomplished what he set out to do. He reached his destination on his 43rd birthday on February 12 and planted a Japanese flag at the summit. Unfortunately, the journey back proved more challenging than the ascent. On February 13, he radioed news of his achievement, but soon all contact with him was lost. Though his diary and other personal belongings were recovered from a snow cave on Denali, the explorer was never found. Today he’s revered as a hero in his home country of Japan, and there’s a museum dedicated to his achievements in Tokyo.

7. Percy Fawcett

Unlike the other explorers on this list, Percy Fawcett was searching for something that’s never been proven to exist. While mapping the Amazon rainforest in the early 20th century, he became convinced of the existence of an ancient jungle city he dubbed Z. In the 1920s, he organized several expeditions with the goal of locating the lost ruins. For his final trip in 1925, he brought along his son, Jack, and his son’s friend, Raleigh Rimell. He had confidence in the mission, but he also had the foresight to request that no one come looking for them if they didn’t return.

His wishes weren’t honored, unfortunately. In the decades since the team disappeared, over 13 expeditions have tried and failed to find them, leading to the deaths of an additional 100 or so people. As for what happened to Percy Fawcett, some theorists are optimistic. Legends tell of the explorer getting lost on purpose and forming an occult commune in the Amazon, or perhaps assimilating into a local tribe.

8. Eudoxus of Cyzicus

Eudoxus of Cyzicus failed to circumnavigate Africa from Europe in the 2nd century BCE. He probably wasn’t the first to attempt the journey, but he may have been the first one to get lost trying. The Greek navigator had already made two successful trips to India via the Red Sea for Egypt. According to Strabo, on the second of these trips, Eudoxus was driven off course and landed somewhere on the east coast of Africa.

There, he found remnants of a shipwreck. Eudoxus concluded that it came from a ship that had rounded the southern tip of Africa and crashed. So he organized a fleet of three ships to leave from present-day Cádiz in Spain. He ran aground on his first attempt, but that wasn’t enough to convince him to call off the journey.

Maybe it should have been: After embarking on that second journey, he was never seen again. It turns out Eudoxus was centuries ahead of his time; it wasn’t until 1488 CE that Bartolomeu Dias became the first European explorer confirmed to have rounded Africa’s southernmost point.

9. John Franklin

In 1845, explorer John Franklin left Britain with more than 100 crew members in search of the Northwest Passage. His two ships—the HMS Terror and HMS Erebus—disappeared in the Canadian Arctic, making the Franklin expedition one of the most infamous doomed voyages in history. Later investigations determined that the vessels had become stranded in sea ice. After Captain Franklin died suddenly in 1847, his surviving crew abandoned the ships and set off to get help on foot.

For decades, it was thought that the ships and their crews had vanished without a trace. Then, in 2014, Inuit and Parks Canada archaeologists discovered the wreck of Erebus in Victoria Strait. The Terror's remains were found off King William Island two years later in Terror Bay.

The discovery of the ships finally brought some closure to one of the greatest mysteries in Arctic exploration's history. Bones of crew members have also been found, one of which has been identified using their descendant’s DNA. But the whereabouts of the remains of most of the expedition members—including John Franklin—are unknown.

10. Roald Amundsen

Unfortunately, many of the explorers on this list are most famous for getting lost—but that isn't the case with Roald Amundsen. Where Franklin had tragically failed decades earlier, the Norwegian gained renown for leading the first expedition to successfully traverse the Northwest Passage by boat in 1905, and in 1911, a team he led became the first group to reach the South Pole.

For Amundsen’s final excursion, in 1928, he boarded a Latham 47 flying boat with five additional men. He wouldn't be exploring new frontiers this time around. Instead, the party set out into the Arctic with hopes of rescuing the crew of the airship Italia, which had crashed on a return trip from the North Pole. Amundsen had had a contentious relationship with Italia's captain, Umberto Nobile, dating back to a dispute over who should get primary credit for their joint expedition to the North Pole a few years earlier.

Despite their history, Amundsen decided to lead a rescue mission. Nobile was eventually rescued by a different party, but Amundsen and his crew never returned home. Parts of Amundsen’s aircraft were later discovered, indicating that it had crashed in the Barents Sea, but definitive evidence of the crew’s fate or the location of their remains have never been found.

This story was adapted from an episode of The List Show on YouTube.

This article was originally published on www.mentalfloss.com as 10 Explorers Who Vanished Without a Trace.