Cheongok Golden Bat Cave in Donghae is the only natural cave in Korea located in a downtown area. Estimated to have been created 400 to 500 million years ago, the cave is known to serve as a habitat for the endangered golden bats. The cave's total length stretches for 1,510 meters, with only 810 meters of the cave open the public while the rest of cave remains protected for preservation purposes. 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. The cave's unique features provide a grand spectacle for tourists and great speleological samples for researchers. A 785-meter walkway was made using the sinkhole created by dissolved limestone to help visitors get a better understanding of cave formations.