1 - A giant cave column swaged in
flowstone towers over explorers swimming through the depths of
Hang Ken, one of 20 new caves discovered last year in Vietnam.
2 - A climber ascends a shaft of
light in Loong Con, where humidity rises into cool air and forms
clouds inside the cave.
3 - 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.
4 - 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.
5 - 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.
6 - Going underground, expedition
members enter Hang En, a cave tunneled out by the Rao Thuong
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.
7 - Headroom shrinks in the middle
of Hang En as cavers pass beneath a ceiling scalloped by eons of
floodwater rushing past. The river shortly reemerges onto the
surface, then burrows into Hang Son Doong after a few miles.
8 - 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.
9 - Moss-slick boulders and a
30-foot drop test author Mark Jenkins at the forest-shrouded
entrance to Hang Son Doong.
"Even though these caves are
huge, they're practically invisible until you're right in
front of them," Jenkins says.
Hunters have found caves by spotting
winds gusting from underground openings.
10 - Hang Son Doong's airy chambers
sprout life where light enters from above - a different world
from the bare, cramped, pitch-black spaces familiar to most
cavers. Ferns and other greenery colonize rimstone.
In the jungles directly beneath roof
openings, explorers have seen monkeys, snakes, and birds.
11 - Rare cave pearls fill dried-out
terrace pools near the Garden of Edam in Hang Son Doong.
This unusually large collection of
stone spheres formed drip by drip over the centuries as calcite
crystals left behind by water layered themselves around grains
of sand, enlarging over time.
12 - 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
13 - Like a castle on a knoll, a
rock formation shines beneath a skylight in Hang Son Doong. A
storm had just filled the pool, signaling that exploring season
was coming to an end.
14 - The trickiest challenge for the
expedition team was to find a way over the Great Wall of
Vietnam, an overhanging mass of flowstone that blocked the way
deep inside Hang Son Doong.
Climbing specialists "Sweeny"
Sewell and Howard Clarke here work on anchoring
bolts to the slippery, porous rock to support the weight of
climbers using ropes.
Once over the wall, the expedition
team discovered a second entrance into the cave.
15 - Dubbed the Great Wall of
Vietnam, a 200-foot cliff halted the advance of the first team
to enter Hang Son Doong, in 2009. When explorers returned,
Sewell drilled bolts for climbers to scale the obstacle with
A white streak below, to his right,
marks how high water rises during the wet season.
16 - "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
17 - In the dry season, from
November to April, a caver can safely explore Hang Ken, with its
shallow pools. Come the monsoon, the underground river swells
and floods the passages, making the cave impassable.
18 - Taking the only way in, a
climber descends 225 feet by rope into Hang Loong Con. A survey
party discovered the cave in 2010, hoping it would connect with
the enormous Hang Son Doong.
A wall of boulders soon blocked the
way, but a powerful draft indicated that a large cavern lay on
the other side.
19 - Streams of light from the
surface unveil stalagmites fat and thin on the floor of Hang
Cavers called the new find the