A bunch of Spanish 20somethings — two girls and three guys — head to a remote island for a camping getaway. One of them has brought along his videocamera, so he can post stuff to his blog later, and at first it’s all drunken idiocy round the campfire and some “hilarious” sneaking up on in-tent sexytimes. But then one of them finds a cave entrance and is all, “Hey, guys, let’s explore the depths of this subterranean maze without any equipment whatsoever except a couple of flashlights!” Soon enough, they’re lost, with no idea which way the surface is. There’s nothing supernatural going on here, just an ever increasing dread as they wander, or more frequently crawl, through puddles and over razor-sharp rocks, and director Alfredo Montero — who cowrote the script with Javier Gullón (Enemy) — effectively creates an atmosphere of physical claustrophobia and psychological terror as friendships fray in the dark and stress and fear brings out the worst in everyone. But you’ve seen this all before, and the mood is overwhelmed by an eventual cheating of the found-footage conceit and a self-awareness that does not excuse its clichés.