James Cameron is obsessed with the Titanic, too, and his fascination and passion exudes from Ghosts. Driven by technological advances and the pressures of time -- in only a few short years the remains of the Titanic will collapse and no longer be recognizable -- Cameron went back 12,000 feet under the North Atlantic with better and cooler toys than he had on his first dive, in 1995. Some of the footage from that dive he incorporated into that big movie of his, and while his 1997 dramatization drew a lot of its emotional heft from its fictional characters, this documentary needs only reality to stun.

Like a real-life reenactment of the framing story of the 1997 film -- in which Bill Paxton's contemporary salvager dives in mini subs to the wreck and explores with robotic cameras -- Ghosts uses the latest in underwater photography, robot cameras designed by Cameron's brother Mike, to investigate the wreck in ways that weren't possible even eight years ago. The little bots, named Jake and Elwood, zoom right into what's left of staterooms and ballrooms, and it's astounding what's left: a brass bed that Molly Brown slept in, a bowler hat, a stained-glass window, a shoe. It's heart-stopping and chills-inducing to see the actual ship, and the film's gimmicks are never gimmicky. Computer-generated overlays that let us know where on the ship we are amidst the "rusticle"-encrusted wreck occasionally give way to ghostly images of Edwardian swells and ragged immigrants on her decks -- oh, and it's all in 3D IMAX, too -- and it all only makes the experience more profoundly moving.

There are historians and marine biologists and the like along on the many dives Cameron and his crew made in the late summer of 2001, but our real entree into the literal awesomeness of the experience is through Cameron pal Paxton (Frailty, Vertical Limit), who's also along for many of the rides. Paxton's scenes in Titanic were all shot in a tank, not two-and-a-half miles down in the crushing depths of a frigid ocean, and as Paxton amusingly demonstrates here, he's nowhere near the imperturbable adventurer his Brock Lovett was. He oohs and aahs in all the places the audience does, and gives voice to the same fears we would, too, sitting in a little tin can way down there, and it's his reactions -- as much as the absorbing you-are-thereness of the extension into the third dimension -- that make this extraordinary venture real for us.

Ghosts of the Abyss is simply spectacular -- it seems that each new IMAX movie tops all that have come before -- and it ends up as so much more than merely a cool sea quest. After a day of technological triumph and daring exploits down at the wreck, the scientific team and camera crews rise to the surface to discover that danger and disaster on an enormous scale haven't been relegated to the past. Like Cameron's fictional version, this trip back to Titanic connects us to the past, and the past to the present, in ways we never expected when we embarked upon the journey.