Houping Tiankeng Group is the core zone of the world Natural Heritage of karst in Wulong. It’s 70 kilometres far from Wulong and covers an area of 38 square kilometers. It’s the only Tiankeng group caused by the erosion of surface water found in the world and is the geological historical remains that is rarely seen and has a high value for scientific investigation. There are various kinds of Tiankengs, which are surrounded by steep cliffs. Viewing from the mouth of them, you are unable to tell the depth, which makes them invisible and mysterious.