Sanmenhai scenic area is located in Leye and Fengshan world geopark, which includes one of the largest sinkholes in the world. It is the core area of typical karst landform, including Sanmenhai Karst windows, Feilong through cave, Shegeng through cave, Mawangdong cave, Dayangdong cave and Gantuandong cave. (Photo: Ipanda.com)