It's about a handful of women daredevils who go "caving" in a big unexplored hole/cavern under a mountain. Like it ain't bad enough that they end up trapped down there and wandering around with very little light or supplies, there are some horrific man-eating creatures down there with them. Yikes.
Scary? Oh yes.
BTW, caving is dumb. If you choose to go way under tons of rock and crawl through spaces that barely fit your body, you are dumb. You deserve to get stuck there, have a panic and/or heart attack, have rocks collapse on you, and to experience the many other horrific ways to die after entombing yourself on purpose.