The 3-D in Sanctum is so aggressive and in-your-face it's more like 3 1/2-D. Hallucinatory, annoying, demanding, it all but yells "Look at this!" even when the thing it demands you look at is nothing particularly special. The story of Sanctum could have been told just as well without the 3-D effects. The real problem with Sanctum isn't the 3-D, however, but the one-dimensional characters. For most of the characters, that dimension is insufferable.
The plot is, according to the opening titles, "inspired by a true story." I'm going to guess that the screenwriters, John Garvin and Andrew Wight, embellished the truth a bit, because nobody ever has or ever could talk the way the characters in Sanctum talk. They don't converse so much as spout cliches and bromides, and offer such pearls of wisdom as "Panic's the vulture sits on your shoulder." Weird grammar aside, if a vulture were sitting on your shoulder, it would probably be appropriate to panic, but since Sanctum takes place almost entirely in a subterranean cave, there aren't any vultures about. Lucky for the vultures.
The story takes place in Papua, New Guinea, in a deep, heretofore unexplored cave system called Esa Ala. A team of Australian cave divers is exploring the caves. According to Carl (Ioan Gruffudd), the millionaire who is financing the expedition, "There's no other place on the planet left to explore." I highly doubt that, and I reckon there are lots of places left to explore, but this is the sort of hyperbole the people of Sanctum are given to. Carl is a jerk, in any case, and he brings his mountain-climbing girlfriend Victoria (Alice Parkinson) along on the expedition even though she has no diving experience. She has even less cave diving experience. On the other hand, expedition leader Frank (Richard Roxburgh) has loads of cave diving experience, which has made him an unforgiving S.O.B., a heartless fatalist, a lousy father, and quite unpleasant to be around. "We're bits of dust passing through," he tells the gang, by way of a pep talk. Frank's son Josh (Rhys Wakefield) hates his dad, and for good reason. The only guy who kind of likes Frank is Crazy George (Dan Wylie), who operates a remote-controlled submarine camera called Virgil. (Virgil was probably named after Virgil Brigman, a character in The Abyss, James Cameron's vastly superior underwater adventure movie. Cameron is an executive producer of Sanctum, which makes sense, given the combination of three things he loves: water, diving, and 3-D.)
While Frank and his team are down there exploring, a cyclone floods the caves, trapping them inside, and forcing a grueling, miserable, claustrophobic, and deadly trek through terra incognito. Also aqua incognito. Lots and lots of aqua. (It would be a good idea to not order the large drink if you're going to see this movie.) They climb, crawl, swim, dive, rappel, grunt, yell, complain, cough, argue, and one by one, one way or another, die.
Director Alister Grierson and cinematographer Jules O'Loughlin do an effective job of creating a sense of confinement and doom, and there's some lovely underwater camera work. I appreciate, as well, the effort to explore the mindset of the danger-seeking adventurer, and the different moral landscape encountered in the bowels of the earth, where a mercifully quick death may be the only help available. I could appreciate it much, much more if it had been executed with some insight, subtlety and sensitivity, rather than with bombast and banal platitudes. If only it could have been done without all the cliches, the stereotypes, and the laughably bad dialogue, I might have actually cared whether any of the characters lived or died. A silent, non 3-D version of this movie would be better, so it'll be passable entertainment on DVD, with the sound turned off, particularly for anyone interested in knowing how many different ways there are to die in a big, watery cave. Falling and drowning are the major ones, but you'd be surprised how many lethal hazards there actually are down there.