A group of six friends are heading off on one of those subterranean caving expeditions that just make me crave wide open spaces. The thing is, though, that one of their number takes them to somewhere hitherto unexplored - without telling them - and so once they start to squeeze their bodies and their kit into these unforgiving spaces, they have no idea where they are going nor what to expect. Not long into their expedition, they encounter some cave paintings and signs that perhaps someone had been there before after all, but instead of turning tail and getting back to the surface they press on to encounter something(s) altogether unexpected, gruesome and hungry. Now maybe one day, someone will make a group disaster thriller that presents us with characters about whom we might actually care, but this is certainly not one of them. The group have their standard mix of baggage, dysfunctional relationships, grudges and mistrust but given little effort is made to develop their characterisations we can just sit back and watch some eerily crafted photography, seriously effective acoustics and some inspired use of light and darkness that expose the vulnerabilities of human beings when not aground, up on two legs, with all five senses working in our favour rather than contributing to an increasing degree of panic amidst this more and more hysterical band of women. I wouldn’t say that any of the actors really stand out here, it could be anyone donning the high-vis jackets and carrying a rope. Indeed the personalities here are largely irrelevant to a truly claustrophobically effective story of what lurks beneath and how unwelcoming it can be to those who stray. Will any of them make it back to the daylight? Well, I hope not!