MIAMI -- The explorers battled fat leeches and cliffs so steep and slippery, one false step could mean a plunge of thousands of feet.
They navigated a raging, treacherous river. They even heard rumors of the Dugmas, a cult of females who load their fingernails with snake venom for attacks on outsiders.
It sounds like an Indiana Jones-style adventure, but it was real.
The expedition, sponsored by the National Geographic Society and conducted in November, took four Americans into the inner gorge of the Zangbo River, the world's deepest canyon, in a remote part of Tibet.
The 17-day undertaking was a lesson in endurance, but the reward was extraordinary: the sight of a thundering, 100-foot-high cascade, dubbed Hidden Falls.
What's equally extraordinary is that the existence of a giant waterfall on a major river had yet to be officially recorded. Indeed, on the eve of the 21st century, many unexplored spots exist on the planet, including in North America.
"Have we mapped every single inch of the globe? Certainly, we have not," said Rebecca Martin, director of the National Geographic Society's Expeditions Board. "There are nooks and crannies in the Grand Canyon no one has gotten to."
For sure, the world seems to have become much smaller during the past two centuries.
In 1806, two American explorers, Meriwether Lewis and William Clark, blazed a trail across North America and reached the Pacific. Early in the 20th century, many large patches of jungle in Africa and Asia had not been visited by outsiders.
Now, explorers have reached the highest mountain (Everest, 29,028 feet), the deepest ocean (at the Mariana Trench in the Pacific, 36,198 feet), and the coldest ice field (Polyus Nedostupnosti, Antarctica, minus 72 F annual mean).
In recent decades, seemingly every far-off locale has been charted, visited or analyzed.
Sometimes these locales have been seriously damaged by visitors. Scientists estimate that with an increasing number of people exploring the Amazon, up to 16 percent of the original million-square-mile rain forest has been ravaged.
Adventure travel is the rage. Growing numbers of tourists trek through the Himalayas, while 10,000 tourists visited Antarctica, the most isolated place on the planet, between November and March. This year alone, National Geographic Expeditions will escort travelers to sites as far-flung as the peaks of Nepal and the Yangtze River (also known as the Chang) in China.
Yet hundreds, if not thousands, of peaks and mountain passes are waiting to be mapped.
From Tibet to New Guinea, to central Greenland and remote reaches of Nahanni National Park in Canada's Northwest Territories, to the Arctic and Antarctica, a host of sites have been accessible only to the imagination.
In Africa, explorers haven't completely roamed the Ndoki forest, on the border of Congo and Cameroon. They haven't fully surveyed New Guinea, the world's second-largest island after Greenland. And they haven't scaled all the mountains in the Antarctic, half as big as the United States.
Perhaps the Holy Grail of exploration is the ocean. The sea covers 70 percent of Earth's surface, and 80 percent of it -- packed with little-known plant and animal life -- remains undiscovered.
"You can draw a parallel between the ocean and outer space, because there's so much we still don't know about them," Martin said.
Underwater caves hold a wealth of opportunities for discovery. The world's longest is Nohoch Nah Chich, located in Mexico's Yucatan Peninsula. Only 32 miles of the cave have been charted. Divers believe that much more remains to be documented, but the pitch-black labyrinth can be deadly for a diver who becomes lost and confused.
In the United States, a National Geographic team is creating a three-dimensional computer map of tens of thousands of feet of submerged caves at Wakulla Springs, about 15 miles south of Tallahassee, Fla. The vast network of caverns and grottoes is believed to be the third-largest of its kind in the world.
"This digital mapping is wonderful, and it's going to help people figure out how ground water travels throughout Florida," Martin said.
Mountaintops symbolize the spirit of exploration. All 14 of the world's mountains higher than 8,000 meters, or 26,250 feet, have been scaled.
Mount Everest was conquered in 1953 by Sir Edmund Hillary and his Sherpa guide, Tenzing Norkay. The famous mountain has been climbed so many times that today's challenge comes in trying to break the record for time spent at the summit. The record was set this month by a Nepali Sherpa, Babu Chiri Sherpa, 33, who spent 21 hours atop Everest.
But mountaineers shouldn't be disheartened, because plenty of peaks are waiting to be mastered.
Many unclimbed summits rise above 25,000 feet throughout the Karakoram mountain range in Pakistan, near the borders with Afghanistan and China. Another unclimbed peak is Lhotse Middle, at 27,605 feet, in the Lhotse massif near Mount Everest.
The higher the mountain, the more discoveries explorers seem to reap.
Last month, National Geographic announced the discovery of the bodies of three children found sacrificed atop Argentina's Mount Llullaillaco, the world's highest archaeological site at 22,000 feet.
Located under about five feet of rock and earth, the perfectly preserved bodies apparently had been frozen for more than 500 years, leaving them to appear as though they had just been buried.
"They appear the best preserved of any mummy I've seen," said archaeologist Johan Reinhard, co-leader of the team that discovered the bodies. "Their arms looked perfect, even down to visible hairs."
One of the world's most uncharted places is the island of New Guinea, north of Australia. The eastern part of the island is occupied by the nation of Papua New Guinea, while the western part is Irian Jaya, a province of Indonesia where up to 800 languages are spoken by primitive tribes living on jungle-choked terrain.
One researcher who has roamed Papua New Guinea is Bill Thomas, an anthropologist who grew up in Youngstown, Ohio.
In Papua New Guinea, he lives among the Hewa, eating mostly bananas and sweet potatoes.
"When I am over there, sometimes I forget what a privilege it is to be in a place like that," said Thomas, 44. "But when I'm dead and gone, I'll have done something you only dream about when you're a kid."
While enthusiasm for exploration hasn't diminished, what has changed is the nature of exploration.
Previously, the main goal was to find remote places that had never before been walked on by humans. The emphasis now is on being the first to examine and document sites, including those that have been visited.
"I know of explorers who've been in the most incredibly dense rain forests in South America and hostile desert in Asia where they couldn't imagine any human had ever walked before, but how can we be sure?" asked Martin of the National Geographic Society.
"What's important now is that people go out and record what they see, and to share that with others," she said.
After National Geographic announced November's discovery of Hidden Falls, explorers from Arizona claimed that they had previously visited the lush, subtropical oasis reminiscent of the paradise depicted in the 1937 Frank Capra movie classic, "Lost Horizon," which made Shangri-la a household word. China didn't open the area to Westerners until 1992.
National Geographic officials have never denied that earlier explorers might have been in the gorge; they insist only that their expedition last year was meant to conclusively document the legendary waterfall.
Dueling discoveries are nothing new. For example, Christopher Columbus wasn't the first person to find America, although he's often credited with doing so.
Perhaps a spot no one will fight over is Mount Kailas in southwestern Tibet, a four-mile-high pyramid of ice and rock.
The peak is regarded as the home of Shiva, god of destruction and rebirth, and is the most sacred summit on Earth for both Hindus and Buddhists.
For now, climbing the mountain is forbidden.
Shelley Emling wrote this article for Cox News Service.
Major discoveries of the 20th century
1911 Hiram Bingham discovers Machu Picchu, a 15th century Inca settlement atop the Peruvian Andes.
1922 British archaeologist Howard Carter opens the tomb of Tutankhamen, an Egyptian pharaoh who died in 1325 B.C.
1940 French children looking for their dog come across the Lascaux Cave, whose walls are decorated with paintings and engravings dating from the Ice Age.
1947 Bedouin shepherds discover the Dead Sea Scrolls tucked inside clay jars in the Qumran Cave in Israel.
1953 Mount Everest is scaled by Sir Edmund Hillary and his Sherpa guide, Tenzing Norkay.
1959 Mary Leakey discovers the fossilized skull of a human ancestor who lived 1.8 million years ago in Olduvai Gorge in Tanzania.
1960 The bathyscaph Trieste descends nearly seven miles in the Mariana Trench to the deepest part of the Pacific Ocean.
1969 Astronauts walk on the moon.
1985 French and American oceanographers locate the sunken liner Titanic in the Atlantic Ocean at a depth of about 13,000 feet.
1994 Explorers near France's Ardeche River discover the Chauvet Cave, whose paintings are thought to be at least 30,000 years old.
Source: Cox News Service