Deep in the heart of Vietnam’s mountainous jungles, there lies a subterranean world that seems lost in time. A gargantuan hollow residing in a limestone mountain, Son Doong cave was once entirely hidden from us but is now considered the largest cave in the world.
So, Khanh retraced his steps, found it for a second time, and led them there.
Today, visitors are welcome to explore Son Doong. At the entrance, somewhat forebodingly, one can feel cool air flowing out like breath. The cave has two entrances—one on either end—allowing air to circulate through. Meanwhile, two massive dolines—sections where the cavern’s ceiling has collapsed, exposing the sky above—allow both air and light to penetrate underground. A fine mist caused by evaporation from roaring underground rivers often drifts through the hollow, adding an air of mystery to the experience.
The rock surroundings of Son Doong consist of flawless limestone that was eroded by waters flowing from two neighboring caves, and this river causes Son Doong to grow in size every year. These waterways also connect Son Doong with other subterranean cavities—such as nearby Thung Cave, whose volume is 1.6 million cubic meters—which means that Son Doong could be even larger than first thought.
Gaining entry into the cavity with help from guides, visitors make camp inside its yawning maw. Here begins a four-day trek to the other entrance on the far end. The sight of tiny tents and people inside the cavernous space makes for a mind-boggling size comparison. Breaking camp, they'll soon hear the roaring of underground rivers, cross icy streams, and reach what is the largest stalagmite in the world. A giant mineral column—built from deposits dripping down from the roof of the cave over the course of eons—towers some 260 feet (80 meters) above the cave floor.
Deeper inside, past rivers and fossil-encrusted rocks, light from the first doline can be seen from about a mile away. Meandering through like ants, explorers draw near a surreal sight—like something out of “Jurassic World.” Where at one time a massive section of the cave ceiling collapsed, a canyon-sized window overhead now allows natural light to stream in. At certain times of day, shocks of sunlight angle downward to penetrate the darkness and illuminate mist, thus allowing lush “Jurassic Park”-like flora to thrive in a cave ecosystem. Channeling this prehistoric theme, the doline was dubbed whimsically “Watch Out for Dinosaurs.”
After transiting this wonderland and crossing the cave’s one-mile mark, the adventurers make camp. The next day, they'll reach the second doline, the larger and older of the two, where trees that are 100 feet tall cover an 850-foot-high cone of ancient rubble. The sublime feeling of entering a lost world is palpable. Drawing from this sublimity perhaps, the second doline was dubbed “Garden of Edam.”
Much of Son Doong is permeated by light from these two titanic portals and the entrances on both ends. But beyond the second doline lies the darkest passage, where the cave narrows and a 2,000-foot-long underground lake forces explorers to travel by boat. It was here that the Limberts originally trudged through a hip-deep muddy channel which they dubbed “Passchendaele,” likening it to that World War I battle. Water levels typically rise and fall in Son Doong, depending on the time of year; cave expeditions halt during storm season from September through December, as heavy rains can cause dangerous swells or flooding and water levels may rise by more than 300 feet (some 90 to 100 meters).
Beyond Passchendaele, the Limberts were initially thwarted by a colossal wall of calcite flowstone, barring them from advancing and forcing them to turn back. This natural partition, which they aptly called the “Great Wall of Vietnam,” looms some 300 feet overhead. Gazing upward at this point, no light can penetrate the pitch darkness to find the cavern ceiling above. Today, visitors are helped to scale this challenging obstacle with harnesses, ropes, lamps, and guides. Then finally, they reach daylight and the cavern’s entrance on the other end.
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