Deer & Langs Cave Deer Cave or Bat Cave is the largest cave passage in the world. An underground river once flowed through this area to form a stream passage cave. Langs Cave is a small cave but it has spectacular array of stalactites and stalagmites - with patterns and shapes of colors. To get to Deer & Langs Cave, one has to walk a 3 km of raised plank-walk from the Mulu National Park HQ. A bat observatory platform is located near the entrance of Bat Cave. Here you can observe the million of bats flying out in wiggling ... (more)