Named Clearwater Cave, it is the longest underground cave in Southeast Asia and the eighth longest in the world, stretching 265km beneath the earth in this Unesco World Heritage site.
Known for the beautiful subterranean river that flows through the cave, exploring it is no easy feat: visitors have to climb close to 200 stone steps! Yet every ounce of effort one puts in is rewarded with breathtaking views of nature unmatched anywhere else.
“Clearwater Cave is famous for its beautiful structure and unique flora and fauna. Visitors can enjoy the limestone formations along an 800m trail without needing to venture deeper inside,” said Richie Philip, 35, a Mulu National Park tour guide.
The journey to Clearwater Cave requires a boat ride along the Melinau River, treating visitors to stunning views of limestone cliffs, lush tropical forest, and occasional longhouses of the indigenous people.
After about 15 minutes, a small wooden jetty comes into view – the gateway to Clearwater Cave and the starting point of the true challenge: climbing all those steps to witness the marvel of the subterranean cave.
At the cave entrance, several botanical treasures of Mulu can be sighted, including “Monophyllaea pendula”, a rare plant that produces only a single leaf throughout its life; and the slipper orchid (“Paphiopedilum sanderianum”), an exotic species with long dangling petals that grows only on Borneo’s limestone terrain.
The true reward awaits at the foot of the cave, where visitors can bathe in the crystal-clear, cool river flowing within.
“The cave’s river, which originates from Mount Api and flows into the Melinau River, is home to unique species such as the blind crab, blind catfish and soft-shelled turtle,” Richie noted.
He warned, however, that although the water looks crystal clear, visitors are advised not to drink it as it may be contaminated by bat and swiftlet droppings.
Another unique feature here is the phytokarst rock formations, created in areas of limestone caves where sunlight is present. The rock is eaten away by bacteria, leaving behind sharp spikes that angle towards the daylight.
“The spikes, resembling the pinnacles of Mount Api, add to this area’s spectacular geology,” Richie added.
Visits to Clearwater Cave are often paired with a trip to Wind Cave located nearby. If Clearwater Cave highlights water as its central theme, then Wind Cave showcases natural airflow that can be felt in certain chambers: two elements of nature that complete the unique Mulu experience.