A staggering 3 million wrinkle-lipped bats live here. The bats roost high on the walls and ceilings where they're well protected from the outside elements and safe from predators. And while they're up here the bats produce something very important. This hundred-metre-high mound is made entirely of bat droppings - guano. Its surface is covered by a thick carpet of cockroaches, hundreds of thousands of them. Caves are one of the few habitats on earth not directly powered by sunlight. In the absence of plants this food chain is based on a continuous supply of bat droppings. The cockroaches feed on the guano and anything that falls into it.