Executive producer James Cameron lends his marketable screen credit and the 3D cameras he developed for Avatar to director Alister Grierson’s modestly budgeted Australian disaster thriller, about a spelunking expedition gone awry in the underwater bowels of Papua New Guinea. “Trust the cave; follow the river,” warns grizzled diver extraordinaire Frank McGuire (Richard Roxburgh) after a tropical cyclone collapses the joint, leaving him to baby-sit his Bieber-coifed teen son (Rhys Wakefield), a smug and reckless financier (Ioan Gruffudd), and other one-at-a-time expendables as they make their escape swim. Inspired by co-screenwriter and explorer Andrew Wight’s actual cave- in trauma, Sanctum overeagerly crams in every possible survival fiasco—from blood- bubbling decompression sickness to “meat-grinder” whirlpools, equipment failures, and mercy drownings. Ultimately, the plot-point overload dilutes any palpable sense of dread, excitement, or empathy, and it doesn’t help that all the dialogue acts in service to either patronizing exposition or turgid interpersonal drama (Frank’s kid comes of age after learning his negligent daddy knows poetry, and gee, can that billionaire blowhard be trusted?). Even the added visual dimension, thankfully used more for spatial recognition than splashing at us, can’t compensate for impersonalized characters stuck under rocks. 127 Hours this ain’t.