The underground forest is also known as the "volcanic crater virgin forest", and the area of more than 1,200 square kilometers of Jingbo Lake District is jointly listed as a national nature reserve, located in the Heilongjiang City of Mudanjiang Province, about 50 kilometers northwest of Jingbo Lake, located in the southeast slope of Zhangguangcailing, about 1000 meters above sea level. When visitors set foot on the southeast slope of Zhangguangcailing, along the mountain road, and climbed to the top of the fire, a huge crater suddenly appeared in front of them. According to scientists, after thousands of years of changes, the volcano erupted about 10,000 years ago, forming a strange and rare "underground forest" in the low depression, so it is called the crater virgin forest. These craters are distributed from the northeast to the southwest, in a narrow and long strip of 40 kilometers long and 5 kilometers wide. There are 10. They are between 400 meters and 550 meters in diameter and between 100 meters and 200 meters in depth. Among them, the largest is the crater 3, which is 550 meters in diameter and 200 meters deep. There are different opinions about the cause of the underground forest, which are still difficult to determine. But it is quite reasonable and very convincing. This said that the inner wall rock of the crater, after long-term weathering and denuding, early with ash and other substances into fertile soil, and the flock of birds carrying various plant seeds flying over the crater became natural seeders, so long, the inner wall of the crater, finally full of trees, Formed forest. Because of its special nature, it not only becomes a wonderful scenic spot, but also an ideal scientific research base for Chinese and foreign geographers, historians and biologists.