By contrast, explorers walked 2.8 miles (4.5 kilometers) into Son Doong, in Phong Nha-Ke Bang National Park, before being blocked by seasonal floodwaters—and they think that the passage is even longer.
In addition, for a couple of miles Son Doong reaches more than 460-by-460 feet (140-by-140 meters), said Adam Spillane, a member of the British Cave Research Association expedition that explored the massive cavern. Spillane was in the first of two groups to enter the cave. His team followed the passage as far as a 46-foot-high (14-meter-high) wall.
“The second team that went in got flooded out,” he said. “We’re going back next year to climb that wall and explore the cave further.”
Source: nationalgeographic