It is a UNESCO World Heritage Site that encompasses caves and karst formations in a mountainous equatorial rainforest setting.

The earliest reference to the Mulu caves was in 1858 when Spenser St. John (British Consul in Brunei) mentioned the "detached masses of limestone, much water-worn, with caverns and natural tunnels” in his book Life in the Forests of the Far East.

Spenser tried to ascend Mount Mulu later but failed due to limestone cliffs, dense forests, and sharp pinnacles.

[4] In the 19th century, Charles Hose (an administrator in the Raj of Sarawak) attempted to climb Mount Mulu but failed.

It was only in the 1920s, when a Berawan rhino hunter named Tama Nilong discovered the south-west ridge near the mountain which eventually led to the summit.

In 1932, Tama Nilong led Edward Shackleton during an Oxford University Expedition to the summit of Mount Mulu.

[4] In 1974, Mount Mulu and its surrounding areas were gazetted as a national park by the Sarawak government.

[4] Between 1993 and 2000, British expedition teams explored the eastern flank of Mount Api with several discoveries made in the Hidden Valley.

[4] In 2000, Gunung Mulu national park was declared a UNESCO World Heritage Site.

Covering an area of 52,864 hectares (528.64 km2; 130,630 acres), it is the largest national park open to tourists in Sarawak.

[4] Gunung Mulu National Park is the most studied tropical karst area in the world.

The landforms in the park consists of rugged summits, steep ridges and escarpments, sheer cliffs, gorges, karst towers, caves and terraces, hot springs, floodplains and waterfalls.

These three younger mountains were formed from 40 km band of karstic limestones during the Upper Eocene-Lower Miocene period.

The cave formation was the result of tectonic uplift of the karst at 2 to 5 million years ago.

[8] Other mammals include Sunda pangolin (Manis javanica), tufted ground squirrel (Rheithrosciurus macrotis), silvery gibbon (Hylobates moloch), Malayan sun bear (Helarctis malayanus euryspilos), maroon leaf monkey (Presbytis rubicunda), and yellow-throated marten (Martes flavigula).

Examples of trees found in this region are: Shorea, Durian, Garcinia, Calophyllum and Eugenia.

Among the species that can be found here are: Monophyllae beccarii, Calamus neilsonii, and the endemic palm Salacca rupicola.

Penan people originally maintained a nomadic way of life, but they are now semi-settled around at the southwest portion of the park at Batu Bungan and Long Iman.

The tribesmen usually wear traditional feather hats, loincloths with tattooed drawings on arms, chest and necks.

[5] The Headhunter's Trail is route taken to enter or leave the Gunung Mulu National Park.

The trail starts with a boat ride to Kuala Berar, then trek for two to three hours to reach Camp 5.

The climbers can either choose to stay at a ranger station Nanga Metawai (15 minutes from Kuala Terikan) or a longhouse named Rumah Bala Lesong (three to four hours by longboat).

After that, a boat ride further downriver would reach Nanga Medamit where there is a road leading to Limbang.

After Camp 4, there are a few vertical climbs which requires knotted ropes which eventually leads to the summit.

Visitors are required to organise into groups of ten with visiting intervals of 20 minutes at the four show caves.

It has a visitor registration building, interpretation centre, audio-visual room and washroom facilities.

The 188-room Royal Mulu Resort has an air-conditioned longhouse, a guest house, four cabins and a hostel.

[8] The park can be accessed by air from Miri, Limbang, and Bandar Seri Begawan through the Mulu Airport; or by boat from Marudi through the Tutoh and Baram River.

[26] The Sarawak government denied that the logging activities would affect the ecology of Mulu National Park.

[27] On 15 March 2019, the natives then decided to lodge an official complaint to UNESCO in hopes to bring attention to the issue.