To many in the caving community Mulu is a holy grail, possessing some of the largest and most spectacular caves in the world. As a result the park has been the site of numerous international caving expeditions, which have resulted in the mapping of over 300 kilometres of cave passages. The expeditions have revealed the extent of the Clearwater Cave System within Gunung Api, 108 kilometres of which have been mapped. Spectacular discoveries include the Sarawak Chamber, which at 12 million cubic metres is the world’s largest single cave chamber. Perhaps best known is Deer Cave, the world’s largest cave corridor, which plays witness to a spectacular daily flight of bats from the cave each evening.

The biology of the caves is intriguing and a large number of species have evolved and adapted to this dark world. Huge numbers of cave dwelling bats and swiftlet species are the drivers of a dynamic food web that sees a flow of energy from the rainforest into the caves.

Daily tours with Park Guides are available to all the show caves. Visitors are not permitted to enter any of the caves without a guide.