Exploring Mulu Caves National Park, Malaysia
October 2025: A Long-Awaited Journey into Borneo’s Subterranean World
The Trip That Almost Didn’t Happen
Going to Mulu Caves World Heritage Reserve was a long-awaited dream finally realized. I had originally booked this trip for March 2020, eager to explore one of the world’s greatest cave systems deep in the jungles of Borneo. But just a week before my departure, the world abruptly shut down—COVID-19 brought everything to a standstill, grounding planes and freezing travel plans everywhere.
Five Years Later—A Promise Kept
I’m not one to give up easily. Five years later, I finally returned to Mulu, this time with a group of close friends who shared my love for wild places and raw adventure. The wait only made the experience sweeter.
Mulu Lives Up to the Legend
We spent four nights and five days in Mulu, and it exceeded every expectation. From its towering rainforest cliffs and underground rivers to its vast cathedral-like caverns, this remote corner of Sarawak, Malaysia truly earns its title as a UNESCO World Heritage Site.
Location of Gunung Mulu Caves World Heritage Area
The Heart of Borneo’s Wilderness
Mulu World Heritage Area is one of those rare places where nature still rules. The park protects a vast swathe of old-growth Bornean rainforest and dramatic limestone karst mountains, covering an area roughly the size of Yosemite National Park. Within this untouched wilderness thrive countless species of wildlife and insects—many still unknown to science—both in the dense forests and deep within the caves themselves.
Returning to Borneo
I had explored the mountainous rainforests in the heart of Borneo twenty years earlier during a five-day trek through the Maliau Basin, one of the most remote and pristine ecosystems I’d ever experienced. That expedition left a deep mark on me. I fell in love with the Bornean rainforest—its raw beauty, its constant hum of life, and its sense of mystery. Ever since then, I had dreamed of returning to experience more of its wild biodiversity.
One of the World’s Great Cave Systems
The caves of Mulu rank among the largest and most spectacular on Earth. Some chambers are so massive they could swallow entire city blocks, while others are intricate mazes of crystal-lined passages, underground rivers, and ancient formations carved over millions of years.
Remote by Design
Mulu’s remoteness only adds to its allure. There are no roads connecting it to the outside world. The only way in for most visitors is by a small turboprop plane, which lands on a short airstrip surrounded by jungle. Inside the park, a few dirt tracks connect key areas, but most transportation is still done by longboat—the same way local Penan and Berawan tribes travel between their riverside villages.
Adventure Awaits
For me, what made Mulu truly special wasn’t just its isolation—it was its sense of adventure. The park offers endless opportunities to explore wild caves, trek through pristine rainforest, and navigate jungle rivers, all under the guidance of experienced park rangers. It’s the kind of place that rekindles a pure, childlike sense of wonder—the thrill of exploring a world few others ever see.
A manta ray that emerged beneath us
Comfort in the Jungle
Where Simplicity Meets Unexpected Luxury
The Village of Mulu
Mulu is a small, spread-out village set along a winding river, with a single narrow road connecting the airport to a handful of guesthouses, the national park headquarters, a tiny market, and a nearby tribal village. The community is home to Indigenous people who have lived in the region long before the park was established. Many now work as rangers, boat operators, or guides—helping visitors experience the same wild landscapes their ancestors have known for generations.
The village itself is very modest, even by Malaysian standards, and its simplicity contrasts sharply with the grandeur of the surrounding rainforest and cave systems.
Days in the Jungle
During the day we sweltered in tropical forests and waded through muddy caves, constantly harassed by clouds of biting insects. Each day was a test of endurance—humid, muddy, and full of raw adventure.
Nights of Comfort
When night fell, we returned to the unexpected comfort of five-star luxury at the Marriott Hotel, located right inside the reserve on the site of the old park headquarters before they were relocated closer to Deer Cave in the 1990s.
We each had our own air-conditioned bungalow built along a raised walkway suspended over the forest. My room even had a bathtub that looked straight out into the jungle—a perfect place to soak and listen to the hum of cicadas and the soft calls of night creatures. There was also a pool for cooling off after long, humid days of exploration.
Morning Rituals
My favorite part of the Mulu Marriott was the enormous breakfast buffet each morning. I made it a habit to show up at 6:15 a.m., even before it officially opened.
A Welcome Contrast
This level of comfort was far from what I was accustomed to on trips like this, but thanks to the generosity of a friend in our group—and the relative affordability of Malaysia—we were able to enjoy it. The contrast between the harsh, humid jungle by day and the cool, air-conditioned comfort of the Marriott by night made the long Pacific flight and the grueling daytime adventures much easier to handle.
Mulu Marriot Hotel
My bathtub in the Mulu Marriot
The Living Jungle
A Symphony of Life and Survival
A World of Hidden Diversity
The best part of Mulu is the sheer diversity of insects, plants, and animal life. There are literally thousands of species living here, each locked in a constant struggle for survival. To endure, every creature has adapted in its own remarkable way—often through camouflage so perfect that even a few feet away, you might never notice what’s right in front of you.
Without the trained eyes of our park rangers, it would have been impossible to spot many of them. Stick insects disguised as twigs, snakes mimicking roots, and spiders blending into bark—all concealed in plain sight. Every step in the forest revealed another hidden marvel of evolution.
The Night Comes Alive
Every day during our trip, we spent hours exploring the jungle, and one evening we joined a ranger-led night hike to experience the forest after dark. As the sun set, the rainforest transformed into a living orchestra—a cacophony of frogs, cicadas, and night birds, each species adding its voice to the humid air.
The Universality of Rainforests
It always amazes me how similar rainforests around the world may appear at first glance—dense green canopies, thick humidity, tangled vines—but when you look a little closer, each is profoundly unique. Mulu’s rainforest, with its limestone mountains, underground rivers, and astonishing biodiversity, is one of nature’s most extraordinary variations on that theme.
Peat forest
Old growth trees
Foot-long stick bug
Leaf insect
Another stick bug
A venomous spider with an egg sac on a night hike
The Living Jungle
A Symphony of Life and Survival
A World of Hidden Diversity
The best part of Mulu is the sheer diversity of insects, plants, and animal life. There are literally thousands of species living here, each locked in a constant struggle for survival. To endure, every creature has adapted in its own remarkable way—often through camouflage so perfect that even a few feet away, you might never notice what’s right in front of you.
Without the trained eyes of our park rangers, it would have been impossible to spot many of them. Stick insects disguised as twigs, snakes mimicking roots, and spiders blending into bark—all concealed in plain sight. Every step in the forest revealed another hidden marvel of evolution.
The Reptiles of Mulu
Then of course there are the lizards and snakes. I spotted a few snakes during our treks, but I always knew there were many more nearby that I didn’t see. In my experience, these reptiles—though often venomous—almost always prefer to avoid human contact. As long as you give them space and respect their territory, the risk of a dangerous encounter is very low. Watching them glide silently through the leaf litter or bask along a sunlit branch is a reminder of how ancient and finely tuned this ecosystem really is.
The Night Comes Alive
Every day during our trip, we spent hours exploring the jungle, and one evening we joined a ranger-led night hike to experience the forest after dark. As the sun set, the rainforest transformed into a living orchestra—a cacophony of frogs, cicadas, and night birds, each species adding its voice to the humid air.
The Universality of Rainforests
It always amazes me how similar rainforests around the world may appear at first glance—dense green canopies, thick humidity, tangled vines—but when you look a little closer, each is profoundly unique. Mulu’s rainforest, with its limestone mountains, underground rivers, and astonishing biodiversity, is one of nature’s most extraordinary variations on that theme.
Green lizard
Lizard perfectly camouflaged with the leaf litter
Tree fog with a very unique chirping sound that filled the forest at night
Tree snake
Into the Depths
Preparing for Sarawak Chamber
Planning the Expedition
I had planned the trip around a two-day jungle hike to Sarawak Chamber, the world’s largest known underground chamber, which required one night of camping deep in the rainforest. This was considered an advanced and potentially dangerous caving route—one that demanded both physical stamina and experience. Before we could attempt it, the park required us to complete an intermediate-level cave as a check-out evaluation with a ranger.
The Warm-Up: Racer Cave
That cave was Racer Cave, a wild, undeveloped system named after the racer snakes that live inside and feed on the swiftlets that nest within the cavern walls. The idea of exploring a dark, twisting cave shared with snakes that hunt birds mid-flight was thrilling enough to make the training day an adventure in itself.
A Visit to Deer Cave
Before venturing into Racer or Sarawak Chamber, we first visited Deer Cave, Mulu’s most famous cavern. Although technically a show cave—with a few walkways and lights installed for tourists—it still feels incredibly wild. The main attraction is its immense scale: it’s one of the largest cave passages in the world and was famously featured in the Planet Earth documentary series.
Reaching the entrance of Deer Cave is half the experience. The trail winds several kilometers through primary rainforest, where monkeys leap overhead, reptiles bask along the path, and countless insects hum in the thick, humid air. This section of the park is the busiest, but given how remote Mulu is—and how long the walk to the cave can be—the crowds never feel overwhelming.
Day One: Arrival and First Descent
After a short but scenic flight from Kota Kinabalu to Mulu, our small plane descended through layers of mist and jungle-clad mountains before landing on the tiny airstrip that serves as the park’s only gateway. Stepping off the plane, the thick humidity hit immediately, carrying the earthy scent of rain and forest.
We checked into the hotel, dropped our bags, and without wasting any time, set off down the jungle trail to Deer Cave that very afternoon. It was the perfect introduction to Mulu—an awe-inspiring combination of rainforest, limestone cliffs, and the mysterious darkness that seemed to swallow the world as we stepped into the cave’s mouth.
Deer cave
Parasitic worms inside the cave that trap and consume insects
Massive chamber inside Deer Cave
Entrance of Deer Cave with fountains of water falling from ceiling
The Bat Exodus
The highlight of Deer Cave is the evening exodus of millions of bats that leave the cave near sunset in search of food. They pour out in waves, forming a long, swirling funnel that snakes through the twilight sky. The column constantly twists and turns as the bats instinctively maneuver to avoid the hawks that swoop in to pick them off.
Watching this spectacle unfold was mesmerizing—a living ribbon of wings stretching across the fading light of the rainforest. It was one of those moments that felt both ancient and eternal, a nightly ritual that has likely continued unchanged for thousands of years.
Bat exodus
Day Two: The Wild Racer Cave
Testing Ourselves Underground
The next day, we set off on our first test—the wild Racer Cave, considered an intermediate-level cave used by the park to evaluate visitors before allowing them to attempt the advanced expeditions like Sarawak Chamber. This cave required climbing, crawling, and navigating tight spaces without the comfort of built infrastructure. Aside from a few ropes to clip into with a harness, it was all raw limestone and muddy rock. Some sections even required rappelling up steep embankments, which added a satisfying element of challenge.
The Snakes of Racer Cave
I was especially excited for this cave because of its namesake—the nonvenomous racer snakes that inhabit it. These snakes have adapted completely to the darkness, their eyes reduced as they rely on other senses to hunt the cave swiftlets that nest within the cavern walls.
The cave didn’t disappoint. Deep inside, we spotted one of these elusive snakes coiled motionless just inches away from us, perfectly calm and unbothered by our presence. Seeing it there—an apex hunter of the subterranean world—was both eerie and fascinating, a living reminder of how life finds a way to thrive even in total darkness.
Entrance to Racer Cave
Climbing in the cave
One of the tight connections in the cave
Racer snake deep inside the cave without eye pigment, from living in total darkness, adapted to feeding on the cave birds
A Change in Plans
Advice from a Veteran Cave Guide
While in Racer Cave, our ranger guide—one of the original cave guides of Mulu—shared some candid advice that would end up changing our plans. We had originally come to Mulu with the goal of reaching Sarawak Chamber, the world’s largest underground chamber, but after hearing his recommendations, we decided to take a different path.
The Dangers of Sarawak Chamber
He explained that caves in Mulu are generally classified as either dry or wet. Sarawak Chamber is a wet cave, meaning it’s highly sensitive to rainfall. Even a small amount of rain can cause the underground river at its entrance to rise quickly, making it far too dangerous to enter.
During this time of year, the park had been experiencing steady rain, and the ranger warned that the odds of actually reaching Sarawak Chamber were slim. Many visitors, he said, hike four or five grueling hours through the jungle to reach the cave, only to find that the water level is too high and the entrance closed. He didn’t want that to happen to us.
The Wind–Clearwater Connection
Instead, he recommended another advanced route—the Wind–Clearwater Connection Cave—which he described as both more reliable and far more beautiful. It was his personal favorite, featuring long, narrow squeezes, challenging climbs, and underground rivers where we would actually have to swim through the darkness.
He explained that the Wind–Clearwater system can still flood in heavy rain, but it was less likely to be closed than Sarawak Chamber, and at least we would know immediately if it was safe to enter rather than after a long, exhausting hike.
A Welcome Bonus
The decision was an easy one. We opted for the Wind–Clearwater Connection Cave and, as an added bonus, it meant one more comfortable night back at the Marriott instead of camping in the jungle. It was a change of plans that turned out to be one of the best decisions of the trip.
Day Three: The Wind–Clearwater Connection
Into the Heart of the Mountain
The Wind–Clearwater Connection Cave was no joke. It turned out to be one of the single best caving days I have ever experienced in all my cave adventures. We spent nearly the entire day underground, enveloped in total darkness, crawling up and down through chambers that at times resembled vast cathedrals and at other times forced us to squeeze through tunnels barely wide enough for my shoulders to fit. It was raw, physical exploration—wild caving at its finest.
Getting There
Like most places in Mulu, reaching the cave was an adventure in itself. We began by traveling upriver by longboat, gliding past dense jungle and limestone cliffs rising straight out of the water. After disembarking, we hiked through humid rainforest until we reached the entrance to Wind Cave, beginning in the show cave section before leaving the comfort of the boardwalk and entering the true wilderness of the cave system.
The Sacred Cave
Wind Cave is classified as a dry cave, but that doesn’t mean it’s easy. The air was hot, humid, and heavy—almost suffocating at times. Within minutes we were drenched in sweat as we crawled and climbed deeper into the darkness. The cave holds deep cultural significance for the Indigenous people of the region, who have long regarded it as sacred ground. Archaeological finds, including ancient skeletons, reveal that it was once used as a burial site thousands of years ago.
Like most places in Mulu, we had to reach them by long boat travel
Inside Wind cave
Life in the Darkness
Sharing the Cave with Its Hidden Inhabitants
At times, while traversing the dark reaches of the cave, I would stop just to take in where I was—deep inside a mountain in the heart of Borneo. It was a hostile, alien world, far removed from sunlight and sound, with only my group of friends and a couple of local guides for company. Yet, despite the isolation, we were far from alone.
The cave was alive. Bats darted through the shadows, their wings whispering overhead. Cave swiftlets—tiny birds that nest in the ceilings—flitted about, their calls echoing through the chambers. Massive cave crickets, easily twice the size of those outside, clung to the walls and scattered when our headlamps swept across them.
And then there were the predators of the cave. Each time we turned a corner, the beams of our flashlights would catch small red reflections staring back at us. Those glowing eyes belonged to giant huntsman spiders—massive creatures with leg spans as large as my hand. Mildly venomous but surprisingly docile, they ruled these caves as apex predators.
We encountered them often, and though I nearly placed my gloved hand on one more than once, they always moved away calmly, uninterested in confrontation. For such a menacing-looking spider, their quiet presence added an unexpected sense of peace to the otherwise eerie darkness.
Giant huntsman spider
The Perils of Cave
A Mysterious and Ancient World
Wind Cave was a mysterious, ancient place. We climbed up steep rock faces and descended others, often knowing that a single misstep could have spelled disaster in such an unforgiving environment. The walls were slick with moisture, the air heavy, and every sound echoed endlessly through the darkness. It was humbling to think how deep inside the Earth we were—so far from light and safety.
Our guide, a seasoned ranger, explained that few people ever enter this section of the cave. He himself had only been inside about a dozen times, and the last group to attempt the full Wind–Clearwater connection had done so months earlier. That revelation added a new level of awe—and caution—to every step we took.
At one point, I asked him whether we might encounter a flooded river. He nodded and explained that it was possible if heavy rain fell while we were inside. One group, he recalled, had made it all the way to the river section at the end of the cave, only to be forced to turn back when the water suddenly rose from a downpour outside.
I imagined how crushing that must have felt—after hours of crawling and climbing in stifling heat and humidity—only to have the exit blocked. We were all silently hoping for clear skies, not just for safety, but because the thought of cooling off in the underground river after the suffocating first half of the cave was all the motivation we needed to keep going.
Me in front of a massive stalagmite
Wes negotiating some cave formations
Inside one of the chamber rooms
Common scene inside the cave
The Connection
Crossing from Wind to Clearwater
I soon realized why this route is called the Wind–Clearwater River Cave Connection. Wind Cave, the dry portion, links to Clearwater Cave—the longest known river cave in Southeast Asia, still not fully explored and believed to stretch more than a hundred miles into the heart of the mountain.
To travel between the two, we had to pass through three extremely tight connection tunnels, a mix of vertical and horizontal passages that took thirty to forty minutes each to navigate. These were narrow, contorted squeezes—barely large enough for my shoulders to fit through. At times, the limestone pressed against both sides of my body, forcing me to exhale just to inch forward.
Because the tunnels were too small to crawl through with our packs on, we had to form a backpack chain—handing them one by one to the person ahead of us, inching them forward through the constricted space. It was challenging, slow, and at times deeply claustrophobic, but also incredibly rewarding.
Emerging from each passage felt like breaking through into another world—one step closer to the hidden river that carved this vast subterranean labyrinth. This section, despite its difficulty, became one of the most memorable highlights of the entire Mulu expedition.
Wes and I in one of the connections
Me descending into one of the connections
The Underground River
Into the Waters of Clearwater Cave
After what felt like forever traversing the dry passages of Wind Cave—carefully climbing over jagged limestone where a single slip could have meant serious injury—we finally emerged into Clearwater Cave beside the cool, rushing river. The sight stopped us in our tracks. The river was enormous—far larger than any underground river I had ever seen—and its water shimmered a clear turquoise, glowing faintly in the beams of our headlamps.
We waded in immediately, letting the cold water wash away the exhaustion and humidity of the previous hours. But the journey wasn’t over. We still had more than an hour of caving left, following the river downstream toward the exit. At times we could walk along the banks, but often the path disappeared and we had to swim across deep sections of the river, keeping our dry bags above the surface.
A Surreal Pause in the Dark
At one point, I decided we needed to stop and simply appreciate where we were. We dropped our bags and jumped into a deep pool of crystal-clear water, floating silently beneath a cathedral of rock. We turned off our lights and sat there in total darkness, listening to the sound of the underground river echo through the chamber.
It was one of those surreal travel moments that makes every hardship—the heat, the insects, the exhaustion—completely worth it.
The Return to Daylight
Eventually, we pressed on, following the river until we saw faint light ahead. We finally emerged into daylight, stepping out into a wide river that had risen dramatically since morning. Our boatman, waiting patiently on the bank, told us it had poured rain while we were underground and the water level had climbed fast.
We realized how lucky we’d been—had we entered the cave any later, the river might have flooded, cutting off our exit. And had we chosen Sarawak Chamber instead, there’s no way we could have entered at all.
It had been an extraordinary day—one of my greatest caving adventures yet—and as we motored back down the river to the Marriott, I couldn’t help but smile at the thought of returning to an air-conditioned room and a warm meal after so many hours in the depths of the Earth.
Wes walking the Clearwater River inside the cave
One of our cave guides
Wes swimming in the river inside the cave
Day Four: The Penan Longhouse
Visiting Long Iman Village
Now that we had gained an extra day in Mulu because of our change in plans, we decided to spend it learning more about the people who call this remote wilderness home. We arranged a visit to an Indigenous village and a traditional longhouse—communal homes found throughout Borneo that can house dozens of families under a single roof.
We visited Long Iman, a Penan settlement located along the river within Gunung Mulu National Park. The Penan are one of the last remaining semi-nomadic tribes of Borneo, with deep ancestral ties to the rainforest. Many now live in small villages like Long Iman, balancing their traditional ways with the modern world.
The Longhouse and the Waterfall Hike
At Long Iman, we were welcomed warmly by local families and shown around their longhouse—a wooden structure raised on stilts, with shared walkways and rooms opening onto a central communal area. It was fascinating to see how daily life unfolded in such harmony with the surrounding forest.
With a Penan guide leading the way, we then set out on a one-hour hike through primary rainforest to a nearby waterfall. The trail was lush and alive with sounds—cicadas, frogs, and the distant calls of hornbills echoing through the canopy.
When we reached the waterfall, we wasted no time plunging into its cool, clear waters. After the heat and humidity of Mulu’s caves, swimming beneath that cascading jungle waterfall felt absolutely incredible—a refreshing and peaceful end to our adventures in the heart of Borneo.
Long house
Inside the longhouse in the communal area
Our Penang guide
The amazing waterfall with the natural water back massage in the middle pool section which we all tried out
Day Five: Leaving Mulu
From the Heart of Borneo to the Next Frontier
After four unforgettable days in Mulu, we took it easy on our final morning. The sounds of the jungle were still heavy in the air as we packed up and headed to the small airstrip for our short flight to Miri—the nearest city, about a hundred miles away across a sea of rainforest.
From Miri, we met our car and driver and began the drive north across the border into Brunei, where we would catch our evening flight to Subawa, Indonesia. There we spent the night before continuing on to Samarinda the next morning, and then onward to Kutai National Park in Kalimantan, Indonesia.
It was a long travel day, but filled with anticipation. Ahead of us lay the next chapter of the journey—trekking deep into the forests of Kalimantan in search of wild orangutans, one of the world’s most extraordinary and endangered species. As the plane lifted off from Mulu, the endless canopy of the Bornean rainforest stretched beneath us, and I couldn’t help but feel grateful for the days we had just experienced in one of the planet’s most magical and remote places.