Introduction to couple's marriage: At a depth of 200 meters at the entrance of Tianchi Chinaogou, there are two tall winter melon poplars, standing like a "couple" in the jungle, one big and one small. The largest one has a diameter at breast height of about 157 centimeters, a height of about 20 meters, and is more than 300 years old; the smaller one has a diameter at breast height of 86 centimeters, a height of about 16 meters, and is 140 years old. They are entangled with each other, and people call it "husband and wife".