Mulu Caves

More than 300 km worth of passages make up the Mulu Caves complex, which also includes one of the world’s largest cavern passages, Deer Cave (which can fit London‘s St Pauls Cathedral inside it five times over). The Mulu Caves began to form over five million years ago when running water began to forge a path between the limestone and sandstone of the mountain’s interior. It is continuing to grow in the same way, slowly developing, as rivers carve their way through the underground cathedrals and redistribute the limestone from the walls and floors to the tips of the stalactites.
Millions of bats live in the complex and in the evenings they depart on mass to feed. To enter the cave system you can either walk along a long wooden bridge walkway just off the ground through an ancient forest and limestone flats or go on a longboat trip to the lower caves. Most of the system is accessible only to experienced cavers, but four caves have been set up as show caves with good lighting and easy access.