In the spring of 2009, British scientist Jonathan Sims was a member of the first expedition to enter Hang Son Doong, or “mountain river cave,” in a remote part of central Vietnam. Hidden in rugged Phong Nha-Ke Bang National Park near the border with Laos, the cave is part of a network of 150 or so caves, many still not surveyed, in the Annamite Mountains.
There’s a jungle inside Vietnam’s mammoth cavern. A skyscraper could fit too. And the end is out of sight.
A giant cave column swagged in flowstone towers over explorers swimming through the depths of Hang Ken, one of 20 new caves discovered last year in Vietnam.
A half-mile block of 40-story buildings could fit inside this lit stretch of Hang Son Doong, which may be the world’s biggest subterranean passage.
Mist sweeps past the hills of Phong Nha-Ke Bang National Park, its 330 square miles set aside in 2001 to protect one of Asia’s largest cave systems. During the Vietnam War, North Vietnamese soldiers hid in caves from U.S. air strikes. Bomb craters now serve as fishponds.
Going underground, expedition members enter Hang En, a cave tunneled out by the Rao Thuong River. Dwindling to a series of ponds during the dry months, the river can rise almost 300 feet during the flood season, covering the rocks where cavers stand.
Like a petrified waterfall, a cascade of fluted limestone, greened by algae, stops awestruck cavers in their tracks. They’re near the exit of Hang En.
Navigating an algae-skinned maze, expedition organizers Deb and Howard Limbert lead the way across a sculpted cavescape in Hang Son Doong. Ribs form as calcite-rich water overflows pools.
“It sounded like a roaring train,” said “Sweeny” Sewell, describing the noise a second before a waterfall exploded into Hang Son Doong through the Watch Out for Dinosaurs doline, or sinkhole opening. A rare dry-season downpour produced the thundering runoff. Were the cavers scared of drowning? “Maybe if it were a smaller cave,” said expedition leader Howard Limbert, “but not here.”
A jungle inside a cave? A roof collapse long ago in Hang Son Doong let in light; plants thickly followed. As “Sweeny” Sewell climbs to the surface, hikers struggle through the wryly named Garden of Edam.