Water has worked wonders on the karst limestone landscape of Gunung Mulu in Sarawak; millions of years of rainfall and runoff have transformed the mountain’s foundations into a wonderland of cave networks.

These aren’t just any old holes in the ground – the caves in Gunung Mulu count among the world’s biggest and best. Sarawak Chamber is the world’s largest known natural cave chamber, its dimensions surpassing 700 metres in length, almost 400 metres in width and 70 meters in height. Deer Cave is the world’s biggest cave passage, at over 270 metres in height.

And that’s just a fraction of Gunung Mulu’s cave network; over 180 miles of caverns snake through the limestone around the park. Fascinating calcium formations, and even prehistoric human artifacts, lurk around the corners – in Racer Cave, a natural “shower head” funnels rainwater into the cave, and the wall of Black Hands Cave shows human hand impressions.

Caves this massive also shelter equally massive populations of bats, which in Gunung Mulu number in the millions, with twelve recorded species making their home in the depths.  

Gunung Mulu’s caves are open to the public, but regulations require that you book a guide to accompany you inside. The park has four “show” caves for the general public – these caves have pathways, railings and artificial lighting. You can also make a prior reservation to enter the “wild caves” (i.e. caves lacking the “show” caves’ creature comforts) as part of a guided adventure tour.

You’ll be required to register at the park headquarters, and pay fees for park entry and the services for a guide.