Deer Cave & Lang Cave

Gunung Mulu National Park

A 3km walk through the rainforest takes you to these adjacent caverns. Deer Cave – over 2km long and 174m high – is the world’s largest cave passage open to the public, while Lang Cave – more understated in its proportions – contains interesting stalactites and stalagmites. Be sure to stay on for the 'bat exodus' at dusk.

Deer Cave is home to 2 to 3 million bats, belonging to 12 species (more than in any other single cave in the world), who cling to the roof in a seething black mass as they gear up for their evening prowl. Every day between 4pm and 6pm (unless it’s raining), millions of bats exit the cave in spiralling, twirling clouds that look a bit like swarms of cartoon bees. It’s an awe-inspiring sight when viewed from the park's bat observatory, a kind of amphitheatre outside the cave. The bats’ corkscrew trajectory is designed to foil the dinner plans of bat hawks perched on the surrounding cliffs.

The record is silent on who did the calculations or how, but it’s said that Deer Cave’s bats devour 30 tons of mosquitoes every night. If it’s raining the bats usually stay home because echolocation (the way they find prey) is not very good at homing in on flying insects amid an onslaught of raindrops.

Count on getting back to park HQ at around 7pm; bring a torch for the walk back.