‘All sense of time and direction is lost,' said Wexas Honorary President Robin Hanbury-Tenison in his book Mulu: the Rainforest. His words are more than mere hyperbole, for the landscape here - which includes the world's largest limestone cave system - is at least five million years old, and new plant and animal species continue to be discovered year after year.
At the park's centre is towering Gunung Mulu, while all around are razor-sharp peaks, deep forest gorges and vine-tangled jungle home to gibbons, hornbills and 8,000 species of plants and tress.
Tough but rewarding multi-day hikes can be arranged within this UNSECO World Heritage Site - accessed by air from Sarawak's second city, Miri, or via an overland journey by road and boat. One possible trek is along the Headhunters' Trail, which follows an old tribal warpath. Another is to the Pinnacles, limestone towers, some 45 metres high, that protrude from the flanks of Gunung Api (Fire Mountain) like bristles on a giant toothbrush.
Others lead into the vast cave system, the size of which is truly astonishing. There are a number of ‘show caves' open to the public, including Deer Cave, which contains the world's largest single underground passage open to tourists, and Clearwater Cave, which has a wonderful swimming hole outside its entrance.
Experienced cavers could even consider the 12-hour journey to the Sarawak Chamber, which at roughly the size of 16 football pitches is the largest underground chamber in the world.
The distinctive smell you'll encounter underground is caused by the guano of more than two million bats that live in the caves. They emerge each evening to search the jungle for tasty insects, an incredible sight that's not to be missed.