The Caves Of Mulu: World's largest Cavern

In search of 'Guano' (bird dung) deposits (used commercially as fertilizers), a British geologist stumbled upon huge cave openings in Malaysia's Mulu's limestone hills, and little did he know his records and notes would lead to the finding of the World's Largest Cavern.

In 1979, after the tourist hotspot in Sarawak, on the isle of Borneo, was turned into the Gunung Mulu National Park, a crew of British cavers was invited to venture into the cavern and find out what lay within the untouched rain-soaked cliffs.

They foreran that the caves would be sensational because the permeable limestone would have been intensely oxidised by aeons of rain surging into it. The region, settled only by the ancient nomadic Penan people, is challenging, and to reach the major ridge of the cliffs, whose rocky walls ascend sheer from the woodland, the trek had to go through the leech-infested jungle, swampy jungle.

The saw-toothed ridge, about 19 miles (30.4km) long and 2.5 miles (4.2 km) wide, snuggles below the sandstone slopes and shale of 'Gunung' (or Mount) Mulu, after which the national park is called after.

The British cavers discovered a path leading into the ridge from the secluded Valley and called it 'Prediction Cave'. However, not until 1981, when scouring the Lucky Cave, did they cross a passageway almost 1.5 miles (2.3km) long, with many waterfalls and a subterranean canal, and came upon the massive chamber. It proved to be five times more significant than the world's largest known cavern, Carlsbad Cavern in New Mexico.

The Sarawak Chamber is 220ft (67m) lofty at its lowest parts. And this is only half as elevated as St Peter's, and three times as long. At the base there are boulders as big as cottages, which at first the British cavers took to be Giant walls, making it challenging for them to estimate the chamber's sheer size by torchlight.

The British Cavers have now discovered some 25 caves, spiralling and winding for more than 120 miles (192km) underneath the mountains.

As captivating as the caverns themselves is the wildlife within their mystifying depths. At sunset, clouds of wild bats fly out from the caverns to hunt as swiftlets bolt back in and roost in a shady world of venomous centipedes, blind spiders, translucent crabs and white snakes.