THE WORLD’S LONGEST CAVE

VIETNAM

Hang Son Doong, in Vietnam’s Phong Nha-ke Bang National Park, has ceilings so high (600 feet) they could accommodate the Washington Monument. Its widest expanses (450 feet) could fit a pair of Boeing 747s side by side. A shimmering blue river runs through it. Most spectacularly, a jungle flourishes under shafts of sunlight in stretches where the ceiling fell in long ago. You want to go deep? The cave is more than five miles long—about five times longer than its nearest competitor for the world’s longest, Deer Cave in Sarawak, Malaysia. Hang Son Doong—the name means “mountain river cave”—has been open to visitors for only two years. (A tour operator says more people have summited Everest than traversed this underworld.) The cave entrance was discovered in 1991—and promptly lost. Ho Khanh, a local man then in his early 20s, went to the national park in search of aloe, whose resin he planned to sell to perfume makers. After he hiked a dozen fruitless miles, rain clouds gathered and Khanh took cover. “I sat down with my back to a huge boulder, then something strange happened,” he later recalled. “I heard the sound of a strong wind and running water coming from behind me.” Back at his village, Khanh’s report of his thrilling discovery was met with skepticism, which only increased after he failed to find it again. He became a kind of semi-tragic figure—the young man who dreamed he’d found a giant cave. Nearly 20 years later, a team of British cavers recruited Khanh to search for the legendary entrance. They made three expeditions, and found many caves, but not Khanh’s great pit. Finally, he returned to the jungle once more in 2009. “I stopped by a big boulder,” he said. “There was the same strong wind, the sound of water running—i knew I’d found the cave at long last.”

A shaft of sunlight hits a section of the cave, called Watch Out for Dinosaurs, daily around noon.