Gunung Mulu National Park is inscribed as a World Heritage Site on 29 November 2000. It is important both for its high biodiversity and for its karst features.

The 52,864 ha Gunung Mulu National Park contains 17 vegetation zones, exhibiting some 3,500 species of vascular plants. Its palm species are exceptionally rich, with 109 species in 20 genera noted.

Gunung Mulu National Park is dominated by Gunung Mulu, a 2,377 m high pinnacle karst, which is said to be the most cavernous mountain in the world. The park is the most studied tropical karst area in the world. At least 295 km of explored caves provide a spectacular sight and are home to millions of cave swiftlets and bats. The Sarawak Chamber, 600 m by 415 m and 80 m high, is the largest known cave chamber in the world. The Deer Cave measuring 120 to 150 metres in diameter is the world's largest cave passage and at 108 km, Clearwater Cave is the longest cave in Asia, and the eleventh longest cave system in the world.