While there is rainforest at many places on Borneo, the combination of gigantic caves embedded into dense tropical rainforest makes Mulu National Park one of a kind. The dimensions of the whole network of caves that are connected with each other reaches a length of 240 km. While some caves are made accessible to us tourists, many caves still remain to be discovered and cannot be accessed due to various reasons such as being underwater caves or being situated too deep inside the mountains.

During our five-day stay Ilinca and I visited four different caves, and in Clearwater Cave I participated in a guided tour off the tourist path which involved climbing, walking through water, and even swimming in small rivers about 2.5 km inside the mountain in the complete absence of any natural light source. The caves in the park are generally classified in three categories:

• Dry Caves are caves that don’t contain running water anymore. The underground rivers that formed those caves now flow through caves at lower levels. The absence of a river at the cave floor allows the growth of stalagmites and stalactites, making these caves look very beautiful. Lang Cave, Deer Cave and Wind Cave belong into this category.
• Wet Caves still contain a flow of water which continuously makes the cave grow, mostly vertically but also horizontally. Clearwater Cave belongs into this category.
• Underwater Caves are completely filled with water and are located at lower altitudes than wet caves and dry caves. These caves are the least explored ones as diving equipment is necessary to access them and the exploration also involves big risks due to the missing oxygen. Naturally, no such cave could be visited by us tourists.

Exploring Clearwater Cave

The Tourist Section of Clearwater Cave

The entrance to Clearwater Cave is very impressive. It is decorated with various plants, and lots of daylight can enter through the huge hole to illuminate the tourist section that is secured by board walks. The dimensions of Clearwater Cave are very impressive. Over some stairs tourists can reach the crystal clear river that runs through the cave.

Going off the tourist path

Apart from the caves that contain a solid board walk, Mulu National Park also arranges guided adventure caving tours. I participated in one of those tours called Clearwater Revival that started where the tourist section ended in Clearwater Cave. At the end of the boardwalk where the cave started to get dark, we stepped down to the river and started going deeper and deeper inside the mountain. After only a few meters, the daylight from the cave’s entrance was gone and we were completely in the dark, the only source of light were our headlamps.

During the next 1.5 hours, we entered almost two more kilometers into the cave along the river. We were walking on sharp limestone rocks, on slippery mud, sometimes also inside the river. On the way out we could also swim some parts in the river which was especially exciting. Whenever we had to climb over some big rocks along the riverbed or cross the river, fixed ropes were in place, so it was not as difficult as it may sound. At the deepest point in the cave, our guide told us to turn off our lamps. And there we were… 2.5 km inside the mountain, and it was completely dark, we only could hear a few bats and the river flowing through the cave. This was a very impressive moment. Thoughts went through my head, what if I went in here alone and my lamp’s battery died? I would never make it out alive… It was nice to turn on the lamps after one minute again and see the beautiful rainforest when exiting the cave after more than 3 hours in the dark.

Fauna inside a cave

It is hard to imagine that any animals live in such unfriendly conditions, however, we saw several species: bats, crabs, fish, bugs, crickets and giant spiders, some of them with a diameter of around 25 cm. They all adapted to the absence of light.

Wind Cave

Being a dry cave, wind cave was beautifully decorated with stalactites and stalagmites. Its name however it got due to the fact that in the narrowest part of the cave, there is usually a slight breeze because the cave is open in the middle as the rock collapsed there and hence wind is blowing towards the entrance from there.

Lang Cave

Named after the guy who discovered it, Lang Cave is also a dry cave with nice decorations. It was the least spectacular cave I have visited, but as it is neighboring Deer Cave, it was worth a visit as well.

Deer Cave

The last dry cave we visited at Mulu National Park was deer cave. Unlike the name suggests, the cave is not inhabited by deer anymore as they have been hunted down by the local tribes a long time ago.

However, deer cave is home to millions of bats. They all live at the ceiling of the enormous cave during the day, and then in the evening usually all of them fly out to feed from tons of flying insects in the nearby forest. This creates a huge spectacle for visitors that are seated in front of the cave when a black swarm of bats flies out of the cave. However, bats are picky with the weather and they only fly out if it is not raining. This is not mainly because they do not want to get wet, but rather because their ultrasound navigation does not work well in heavy rain.

We were unlucky this day because there was actually rain until shortly before sunset so the bats decided not to fly out (yet). Most likely they have flown out later, but because it was dark already, it was not possible to see them anymore. Nevertheless, Deer Cave was absolutely fascinating as the diameter of the cave was the largest I have ever seen (and the second largest in the world) and we still could witness the presence of the bats because most of the cave floor was covered by huge pile of bat excrements.

The highlight of my stay at Mulu National Park in Borneo was a three day trek and climb to the pinnacles, an interesting limestone rock formation at an altitude of 1200m, embedded in the dense rainforest that covers the plains and mountains at Mulu National Park. A trekking adventure that involved boat transfers on longboats on beautiful jungle rivers, walks through the flat part of the rainforest, and moderate climbs over roots, leaves, and at times slippery limestone, supported by fixed ladders and ropes.

Meeting my companions

This trekking adventure was only available as part of an organized tour and a minimum number of three participants. Unfortunately I could not convince Ilinca to join me, so I subscribed alone for the tour. As the groups will be up to ten people per guide, I was hoping that at least two more people subscribe to the tour, but not too many because the larger the group, the higher the chances to get people on the group I would rather not travel with.

I only met my companions on the morning the trek started: Three girls. I was a bit surprised because I assumed this kind of activity is more of a guy’s thing, but probably I am just too old-fashioned. But of course the surprise was clearly on the positive side. All fun people with their own interesting past. Claire from the UK, and Evelyne and Lucil from the French-speaking part of Switzerland.

Moving to Camp 5

On day one of the trek, we went upriver on a longboat. As the water in rivers through the jungle can be very shallow, longboats are the perfect means of transport as they don’t go deep into the water. But even then sometimes it is necessary for everybody to get out of the boat and push it over the rocks. Luckily for us, there was heavy rain last night and the water levels were high enough to pass without getting wet feet.

After around one hour upriver, we were dropped off in the middle of the rainforest. From there, it was an unguided 10 km walk through the rainforest. Thanks to the heavy rain last night, it was not very hot that day, but still hot enough to arrive soaking wet from sweating at Camp 5.

On the way to Camp 5 we did not see any interesting wildlife, which might also have been due to the talking along the way. The only animals that we noticed were leeches as they were suddenly attached to my socks and trying to make their way through them to suck my blood. Two of them I could stop before they reached their goal, a third one was more successful and at least made me bleed for a while. But I should not complain, because I was carrying special leech socks in my backpack but I was too lazy to put them on.

After 2.5 hours we finally arrived at Camp 5, a forest camp with a surprisingly nice infrastructure such as showers, toilets incl. toilet paper, a kitchen, and dining tables. The only problem: the place was infested with hundreds if not thousands of huge bees which were going after everything sweaty. So the first thing to do was to jump inside the river nearby and was the clothes. Afterwards the situation was slightly better and during the night, the bees also got their well-deserved sleep. We were told afterwards that the main reason the bees are here is not our sweaty trekking gear but the fact that the durian trees nearby were in blossom.

After a simple self-cooked dinner, we met our guide Imran for the climb to the pinnacles the next day. Somehow he felt the need to scare everybody a bit by exaggerating how tough the climb would be and many people already got insured. The next day would show that it was just a normal hike as we have tons of them in the Swiss Alps.

Climbing to the pinnacles

Camp 5 is only located at 150 m above sea level, the pinnacles are at around 1200 m. So we had a 1000 m climb ahead of us. And in contrast to the walk the day before, it only went in one direction: upwards! First we were climbing through dense rainforest on a small path, but the closer we got to the top, we had to climb over rocks and roots. The slippery and risky passages were all secured either by ropes or metal ladders. The most challenging part of the climb however was the heat and humidity, and I was really happy that at least we were walking in the shadows of the trees and not in the sun.

After nearly four hours incl. all breaks, we finally reached the pinnacles. A beautiful view on limestone rocks that have been transformed into sharp needles by the rain, however my expectations were a bit higher. Only for the rocks I would not do that hike again, but the path up through the jungle was really awesome.

On the way down, which took at least as long as the climb, we met a few animals. A snake decided to cross my path about 1m in front of me, and lots of big butterflies, caterpillars, and worms were sitting on trees right next to the path.

Back at Camp 5, the same story as the day before: tons of bees. And the same solution: A quick bath in the river and washing out our clothes.

Returning to Mulu

On day three, we walked back the same 10 km path to the river where we went downstream in a longboat to Mulu National Park’s headquarter. As it had not rained the last two days, the water levels were lower today and at one point everybody had to go out of the boat and push it for about 10m.

At noon, we reached our goal. It was an awesome adventure and we were a great group of companions. And even though the pinnacles alone would not be worth such a trip, it is the whole adventure with sleeping in a jungle camp and the climb up in the rainforest which made this trip an unforgettable adventure.

As part of our stay at the Mulu National Park in Borneo, we not only explored caves as described in another post, but we of course also explored the dense rainforest with its rich flora and fauna. One way of doing this is by going on unguided walks on wooden boardwalks. But as most of the life in a rainforest takes place in the canopies and not on the ground, we wanted to get a monkey’s perspective of the rainforest.

At Mulu National Park, apart from the excellent network of trails, there is also a Canopy Walk where visitors walk up to 35 meters above the forest floor from tree to tree. The canopy walk itself is a series of rope bridges that go from one tree to another. The total length of that walk was 450m, which does not seem like very long, but given that those were all shaky bridges, the walk took much longer than expected.

There is lots of wildlife in the jungle, but also lots of trees and plants that hide them from our sight. I was hoping that from the canopy walk we would spot more animals than when walking on the trails, but in the end we did not see any monkeys or other larger animals this time, and only a few insects, some birds flying by and a small green lizard. Nevertheless, the walk was still very impressive as it gave us a completely new perspective of the jungle.