World Heritage Information


Mulu’s Geo-diversity

Vertical cliffs and incredibly steep slopes reach summit ridges before dropping abruptly down to deep gorges and hidden valleys. Jagged limestone pinnacles, bleached white, spear out of the lush green canopy.

Cave passages twist and wind their way through the mountains, opening into chambers so large they defy description and dwarf you into insignificance.

In landscapes like these we must look to the past to understand what we see today.

Around 60 million years ago deep beneath the sea, one piece of the Earth’s crust began to slide up and over another piece of the Earth’s crust. For 20 million years rock grinding against rock produced a 5 km thick layer of sand which became cemented together as a deposit of sandstone known geologically as the ‘Mulu Formation’, but 40 million years ago it was still beneath an ancient sea teeming with sea life. Coral reef lagoons developed and over another 20 million years these lagoons were filled with layer upon layer of calcium carbonate mud formed from the soluble minerals found in seawater. Mixed with millions upon millions of minute sea shells the layers of calcium carbonate were compressed to become a 1,500 metre thick deposit of limestone known geologically as the ‘Melinau Formation’ and like all limestone it was formed in sea-water and it dissolves in fresh-water.

When the movement of the Australian and Asian landmasses caused the earth’s surface to buckle and fold about 5 million years ago, these sandstone and limestone formations were lifted high above the sea to create the mountains of Mulu and the relentless process of weathering by the elements now began to shape the landscape we see today.

As the rain falls on these limestone mountains, it passes through the soil and into the very small pores and cracks found in the limestone. Seeping and trickling through the limestone, the water gradually dissolves the rock, making these pores and cracks larger and larger to create a remarkable series of cave chambers and passages.

And here at Mulu you’ll find the biggest caves in the World!


Here in the heart of wondrous Borneo, you will be amazed by the rainforest around you. In the humid heat, plant life flourishes everywhere. Many thousands of species of ferns, mosses and flowering plants along with thousands of species of fungi thrive in this complex habitat.

52,000 Hectares of spectacular equatorial rainforest presents visitors to Gunung Mulu World Heritage Area with an outstanding diversity of flora and fauna. This is home to many fauna species from the World’s smallest mammal, the Savi’s Pigmy Shrew, to some of the largest insects on Earth. In the dense foliage secretive macaques, bearded pigs and moon rats hide, blending in so well that we rarely see them among the tall towering trees blocking out the sky with their dense canopy. Richly coloured butterflies glide among trees entwined with lianas, ferns and orchids. The ground is a thick mat of leaves and fresh new seedlings struggling to find their own space. The heartbeat of life is all around you, plants and animals, living, eating and dying.

Strangler figs, spread by fruit-eating birds, begin life germinating high in the canopy. Growing quickly in the sunlight the Strangler sends a shoot down to the ground and then starts to surround the host tree, becoming larger and stronger as it clings to every surface available, strangling the tree in its death grip. Finally, the tree will die and rot away, leaving the fig standing as a shell of the tree’s former shape.

Watch out for the rattan, a thorny vine reaching for the sun, it entwines its way for up to 1000 metres through the trees. This is an important plant used in weaving by the local people, but for the unwary, it’s a painful meeting.

The air is rich with the perfume of 170 species of wild orchids. If you are lucky you will see the famous Slipper Orchids, or you may spot the curious shaped pitcher plants. Mulu is home to 10 species of these insectivorous plants which supplement their diet by eating visiting insects.

Some plants use animals in other ways. One species of ginger, flowers at ground level and exudes a pungent smell. Beetles rolling balls of dung, in which they will later lay their egg, are fooled into thinking there is fresh dung and eagerly seek it out.

The beetle gets no dung, but the flower does get pollinated.

But why is Mulu so diverse?

First there’s the topography with the landscape ranging in altitude from just 50 metres above sea level near park headquarters to the peaks of Gunung Mulu at 2,377 metres, and then we have the unique underground environments of the caves. Combine this with a geology of alluvial clays, sandstone and limestone formations to produce dozens of niches and specialist environments for both plants and animals.