Cheongok Cave (천곡천연동굴) is a limestone cave that extends horizontally for 1,400 meters. Estimated to have been created 400 to 500 million years ago, it is the only natural cave located in a downtown area. The cave features ceiling craters, one of which is the longest in Korea, along with stalactite curtains, travertine terraces, stalactite cascades, and many other fantastic rock formations. It provides a grand spectacle for tourists and great speleological samples for researchers. As the inside of the cave is lined with over 20 types of secondary formations, such as stalactites, stalagmites, and limestone pillars, it is an invaluable resource for earth science education.