Despite the wooden path specially erected to make forest exploration easier, a trek through the Gunung Mulu National Park in Sarawak, Malaysia, is no walk in the park.

The air is warm and the thick canopy of jungle trees is little protection against the oppressive heat of the sun. The stifling humidity of the damp forest air makes me feel unbearably sticky.

Yet, this jungle walk turns out to be an unforgettable experience. My eye is drawn to furry caterpillars in shades of green, orange, and yellow lounging lazily atop tree branches. In the background, birds hum while cicadas screech, and although noisy, the forest orchestra is enchanting.

Exotic species abound in the park

Nature's gem

The Gunung Mulu National Park is a Unesco-designated World Heritage Site, and is also the biggest national park in Malaysia's largest state of Sarawak.

Despite the natural treasures within, the park remained unexplored until the late 1970s when it was first surveyed by Britain's Royal Geographic Society.

Today, the 544 sq-km park is still relatively untouched, partly because it is accessible only by plane and boat. Much of the park comprises virgin rainforest, and it is still home to the last of Sarawak's nomadic tribes, the Penans.

The Mulu Caves

The Mulu Caves are the highlight of the Gunung Mulu National Park

The highlight of the park, however, is the Mulu Caves, an intricate system of caves believed to be the most extensive in the world. To date, only 310km out of a total estimated 900km of its passages have been fully explored.

You can find the world's largest natural cave chamber, which is so huge it can hold more than 47 jumbo jets. Within the Mulu Caves, you will also find the world's largest passage and the longest cave in South-east Asia.

There are three main caves you can explore. The first I visited was the Deer Cave, named after a type of deer that were frequently sighted around the vicinity until they were hunted to extinction some decades ago.

Today, the cave is home to about three million bats, or 40 per cent of the total bat species in the world. During the day, these nocturnal creatures hide behind the cave ceilings. But once the air cools in the evening, they appear, creating a majestic sight as they swoop down in flocks to hunt and feed on the insects that also live in the cave.

The natives still practise traditional hand weaving

Wind Cave is my next stop. Perched high in the midst of the Mulu mountains, getting up there can prove a hassle for the physically challenged. I was huffing and puffing less than halfway up the 10-storey climb. I'm heading for a small section named the King's Chamber, which is filled with stalactites and stalagmites of every shape and size.

My cave exploration ends with the Clearwater Cave, the longest cave passageway in South-east Asia with a clear stream that cuts through its middle and runs for a further 108km. It has never been completely explored from end to end.

These three caves make up less than 50 per cent of the entire area of the Mulu Caves. Instead of simply following designated trails into the caves like what I did, adrenaline junkies can try their hands at adventure caving.

Some of the cave's best kept secrets, such as the hidden pools of crystal clear mountain waters and narrow cave passageways are accessible only if you dare to venture off the beaten path.