This cave is located in a hill 30 metres away from the coast of Hongwon.

The hill, composed of granite cataclasite, was once an islet near the land, and the cave was formed through the age-old erosion. With the islet gaining in above-sea level, the cave grew bigger, and sand from the land and the sea accumulated between the islet and the land, finally linking both.

The cave is in a semicircular shape, the front and the back being vertical.

It is a 10m-long through cave and about 20m2 of its area is filled with seawater.

Where the cave adjoins the sea, it is 12m wide and 9m high.

The cave is academically valuable as it has witnessed rhythmic movements of the earth’s crust, changes in seawater, erosion and sedimentation from the rivers and the sea and adds more beauty to the coastal scenery.