I have also written a review about the sister cave, Hwaseongul. I thoroughly recommend making a booking and visiting Daegeumgul. We had a Korean speaking friend who phoned and made the booking, but maybe you can use a web-site? The cave can only be visited with a guided tour. This is because it was only discovered in 2002 and opened in 2007. The cave features have been heavily protected and are likely the best you will see in Asia or the World. At one point you walk over the fast-flowing underground river, which is thrilling. Some of the stalactites and stalagmites are awesome. You will understand why you can only enter via the monorail penetrating through a tunnel, as the contents must be keenly preserved. In fact you can only enter via a monorail. You cannot walk to the cave entrance. Our tour group was small, only 7 people. The tour is only in Korean, but the features really require no explanation and they speak for themselves. However, our tour guide was a bit sulky and rushed us though the caves. Given the amazing nature of this cave, I feel the operators could do better with their staff recruitment. It felt as though the Guide was doing us a favour by showing us around. Yes, that is true, but some customer training would be good. Don't let that put you off. First visit Hwaseongul, but when you buy your tickets for that cave then make the booking for Daegeumgul for 2 hours later (if you have not already made a booking.