Wailing cave

Arriving at an area near the river the blacksmith gets out of the truck . Giving each a pair of ear plugs he walks towards the river where the cliff wall and a crop of trees meet. 

Wedged behind thick foliage is a crack in the mountain wall. It's just large enough for a person to crawl inside. Following the blacksmith they crouch down and begin to crawl into the crevice. The floor is wet and muddy from the water seeping in. The area gets larger as they crawl deeper into the the cave. After about ten minutes the cave opens up and they can stand. Turning on their flash lights they see the interior of the cave for the first time. 

it's a huge area with a pit in the center. Walking along the thin ledge around the pit the spiral down deeper. 

"What is this place and why must we wear earplugs?" Seo Jun asks telepathically.