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Mulu Cave

The most spectacular caves on earth

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In Borneo, deep in Sarawak’s Gunung Mulu National Park, lie the most spectacular caves on earth. Over millennia the flow of water draining from the slopes of G.Mulu towards the sea has cut deep gorges through the Park’s limestone mountains and, within the rock itself, a complex network of vast caves has been formed.

Since 1978 these caves have been the focus for a succession of expeditions and this website holds a record of the discoveries made during that period.

As we move into the 21st Century, humanity appears to have explored to the limits of our environment. Using technology we can photograph the surface of distant planets, probe the immensity of space, scan the beds of the deepest oceans, image the inside of living bodies and picture the surface of structures to microscopic detail. In such a world, it might be imagined that there is no true exploration left to be done. But this would be untrue.

Under the surface of our planet lies a parallel world, a world of great beauty and mystery formed over thousands of years by the most elemental of forces, the passage of water through rock. This world, the domain of caves, remains largely unexplored.

Gunung Mulu National Park is famous for its limestone karst formations. Features include enormous caves, vast cave networks, rock pinnacles, cliffs and gorges.

Gunung Mulu National Park has the largest known natural chamber or room - Sarawak Chamber, found in Gua Nasib Bagus. It is 2,300 feet (700 m) long, 1,300 feet (396 m) wide and at least 230 feet (70 m) high. It has been said that the chamber is so big that it could accommodate about 40 Boeing 747s, without overlapping their wings. The nearby Deer Cave was, for many years, considered the largest single cave passage in the world.

Api Chamber in Whiterock Cave, Mount Api

Other notable caves in this area are Benarat Cavern, Wind Cave, and Clearwater Cave; which contains parts one of the world's largest underground river systems and is believed to be the largest cave in the world by volume at 30,347,540 m³.

Mulu's limestones belong to the Melinau Formation and their age is between 17 and 40 million years (Late Eocene to Early Miocene).

Stratigraphically below the limestones, and forming the highest peaks in the south east sector of the Park including Gunung Mulu, lies the Mulu Formation (shales and sandstones). The age of these rocks is between 40 and 90 million years (Late Cretaceous to Late Eocene).


Eight species of hornbill have been spotted in Mulu including the Rhinoceros Hornbill Buceros rhinoceros which features on Sarawak state emblem, the White-crowned Hornbill Berenicornis/Aceros comatus and the Helmeted Hornbill Buceros vigil with its large solid casque (bill).

Twenty seven species of bat have been recorded in Mulu. Deer Cave in the southern limestone hills of the park is home to an enormous colony of Wrinkle-lipped bats (Tadarida plicata). The bats exit the cave almost every evening in search of food in a spectacular exodus. A huge mound of guano in the cave is evidence of the size of the bat colony that roosts in the cave's high ceilings.

Mulu's mammals also include the Bearded pig Sus barbatus, the moonrat Echinosorex gymnurus, shrews, the Bornean Tarsier Tarsius bancanus, the long-tailed Macaque Macaca fascicularis, gibbons, squirrels, and three types of deer including the small barking deer and mouse deer. The small Malaysian sun bear Helarctos malayanus, which is the only bear known in South-East Asia, has also been identified in Gunung Mulu National Park.


An upper pitcher of Nepenthes faizaliana from Mount Api. This species is endemic to Gunung Mulu National Park.

Gunung Mulu National Park contains a large number of plant species, including flowering plants, trees, and fungi. Geology, soil types and topography have given rise to a rich tapestry of plant zones and types. On Gunung Mulu itself these include lowland mixed dipterocarp forest, lower montane forest, mossy or upper montane forest and summit zone vegetation on the highest peaks. On the limestones there is lowland limestone forest as well as lower and upper montane limestone forest. Other plant communities dominate the alluvial plains, including kerangas (tropical heath forest) and peatswamp forest.


Mulu is a very inaccessible area; the only practical way of getting to and from it is by air, mainly from Mulu airport, and alternatively, Miri, which is 100 km away. It is possible to travel to the area by riverboat, but it requires a chartered long boat for the last part - and the whole trip by river would take around 12 hours to complete from Miri, while the flight takes only 30 minutes. Prior to the opening of the airport, and the opening of a helipad in 1991, this was the only way to reach the national park.

Excursions to Mulu continues to retain the sense of adventure associated with its original exploration through the provision of adventure caving and other adventure activities. The primary focus however has shifted to the promotion of an awareness of the significance of the park and its environment through the provision of ecotourism activities that foster understanding and appreciation of the parks values. Accommodation is available onsite at Gunung Mulu National Park HQ, as well as Royal Mulu Resort, and the tropical-style boutique hotel The Matumau Lodge. Homestays offered by locals, and other typically cheaper lodging are available across the river.


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Last modified: 11/02/11
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