38 years ago today, on January 5, 1987 (December 6, 1986 lunar calendar), a giant crater was discovered in Inner Mongolia. The "circular water system" crater found in Duolun County and Zhenglan Banner of Xilingol League, Inner Mongolia is the largest of the four craters discovered in our country and the second largest crater in the world. On the Xilingol Grassland of Inner Mongolia Autonomous Region, there is a very special "circular water system". This topography formed hundreds of millions of years ago is a crater left by "aliens" after they arrived in the grassland. This "circular water system" formed by the Luanhe River and the Flash River is located in Duolun County and Zhenglan Banner of Xilingol League, and is integrated with the ruins of the ancient city of Yuandang, which was the temporary capital and accompanying capital of the Yuan Dynasty. Recently, when reporters visited the ruins of the ancient city of Yuan Shang, they specially went to check the crater. A person from the Zhenglanqi Cultural Bureau told reporters that the Luanhe River and the Flash River used to be the annular moat of the ancient city of Yuan Shang. The inner ring diameter of this "annular water system" is 70 kilometers, and the outer ring diameter is 150 kilometers, making it difficult to see the whole picture with the naked eye. It is said that this crater was discovered by satellite. In 1986, Wu Enben, a geologist at the Institute of Mineral Deposit Geology of the Ministry of Geology and Mineral Resources, and others, based on the clues provided by satellite photos, went to Duolun County and Zhenglanqi to conduct field investigations and confirmed that this "annular water system" structure was originally a huge crater remnant of a meteorite explosion. According to geological experts, this crater was formed between the Jurassic and Cretaceous periods, about 140 million years ago, and is one of the four craters discovered in our country. At present, the Yuan Shang site has been listed as a national key cultural relics protection unit and declared a world cultural heritage. Zhenglanqi has also initially developed some Yuan Shang site tourism projects, and has built a number of tourist facilities such as the Yuan Shang Museum and Kublai Khan Summer Palace. In recent years, there has been an endless stream of tourists who have come here. If the crater constructed by the "circular water system" is developed again and a "crater wonder" tourism project is added, it will attract more tourists to visit.