The stunningly beautiful cave scenes are breathtakingly realistic in this James Cameron-produced 3D “inspired by a true story” saga of a cave-diving expedition gone wrong.

The plot and characters, not so much.

It’s the basic “and then there were none” plotline. Foolish humans take big risks, get into trouble, and have to find their way out — literally. At first the group is hard to tell apart, but soon those who are least differentiated either escape or get killed and we are left with the core group. And it isn’t enough that they have to escape from a whole series of life-threatening perils (too wet, too high, too cold, too deep, too far); the experience also has to serve as family and couples therapy as a reluctant young cave-diver has to confront his tough old boot of a father (the expedition leader) and the arrogant, impulsive adrenaline junkie of a funder has to deal with his date on her first-ever cave experience.

Cameron’s use of 3D is splendid on this real-world Pandora. The film conveys the cathedral-like spaciousness, the claustrophobic passageways, and the vertiginous drops of the cave very well. But the structure of the film is so predictable and the characters so thin and unengaging that it feels more like watching people at a theme park than anything with any sense of peril or involvement. The best thing about the dialogue is that the actors’ Australian accents sometimes make it unintelligible. And a painful series of complicated moral choices are deployed for sensation, rather than depth — just like the hubristic expedition itself.