Wild Boar Trench(SANZU Ditch) is situated northwest of Sanbanao and connected to Black Dwart Cave. Composed of cliffs, the ditch is dangerous, deep, curved and about 400 meters long and has a variety of wild plants in it. It is said that mountain pigs were seen in the area, so people called it Sanzu (mountain pig) Ditch.
In addition, according to legend, there was a mountain pig spirit that is hundreds years old and able to change itself into a man formation. One day, the mountain pig spirit saw a female fairy taking a bath in the sea with her clothes left on the shore and then stole the clothes. After taking a bath, the female fairy found her clothes disappeared, which made her unable to return home naked. The female fairy hid herself and cried in the jungle. The mountain pig spirit took the opportunity to ask the female fairy to marry him in return for the clothes. The female fairy pretended to accept the deal and got her clothes back. As soon as the female fairy put on the clothes, she flew away immediately. The mountain pig spirit could not stop missing the female fairy and crying and then died of sadness. According to this legend, people named the place Sanzu Ditch.