Although believed to be as old as nearby Hwanseon-gul, Daegeumgul wasn't discovered until the early 21st century and not opened to the public until 2007. What is unusual about the cave is the amount of water that flows within it creating waterfalls and an underground lake. A 610m-long (6,000-ft.) monorail takes you into the cave, and then you'll see various stalactites creating pillars, shields, and smaller caverns. Only 40 people are allowed in at a time and the entire tour takes about 90 minutes.