A shadow creeping ominously into view through a motel room shower curtain. A swimmer's legs dangling tantalizingly under the water as something big and hungry glides purposefully toward them. A terrorized baby sitter learning that the calls are coming from inside the house. And a close-up of a single frightened, crying eye of a lost camper in her tent at night, her sobs interrupted as she breathlessly whispers to the camera, "What was that?"

These are landmark moments in cinematic horror, the ones that stick in your memory and haunt you long after the house lights go up, and they only come along once in a generation. If you don't recognize the last one, it's because it's from "The Blair Witch Project," the darling of Sundance and Cannes that's already being buzzed as the scariest movie ever made. That, of course, is debatable -- but the fact that a shoestring-budget mockumentary with no name stars, no special effects, no rivers of bloody gore and not even a musical score can be this spooky is a testament to the storytelling ability of the filmmakers, and to their trust in the audience's imagination. It's been a long time since a movie did so much by showing so little.

The back story, outlined in the film's opening, is that three student filmmakers went into the Maryland woods to make a documentary about the mysterious, gruesome legacy of a legendary local witch and never returned. A year later, their footage was found. What we see next is a chronicle of the group's harrowing last days as they themselves filmed them, a kind of "Real World" meets "The Texas Chainsaw Massacre," with a splash of "Deliverance." It's an ingenious device, one that efficiently and economically exploits our cultural immersion in reality TV and recalls our own amateurish and shaky home videos. It's at once familiar and disquietingly surprising. In the 20 years since Michael Myers first donned a mask and heavily breathed his way through "Halloween," the standard has been for horror movies to unfold from the killers' perspective. But "The Blair Witch Project" finally turns the camera around and forces us to see through the eyes of the victims. It's a far scarier place to be.

Heather, Josh and Mike (in yet another authenticity twist, all three actors perform under their real names here) rapidly devolve from a cocky trio of would-be auteurs into three frayed, fearful individuals when they realize they are lost -- but not alone -- in the woods. Mysterious piles of rocks appear in their paths. Strange voices seem to be calling from points unknown. And signs of other unfriendly life become more obvious with the passing of each desperate day. The prologue of the film makes the characters' doom a fait accompli, and this information gives "Blair Witch" a new kind of suspense. In conventional horror, we know how things are going to happen (watch out for the guy with the burned face and the razors for nails, dude); we just don't know to whom they're going to happen. Here, we are fully aware that nobody -- not even the plucky girl -- is coming back from that camping trip. The suffocating terror, and the gloomy poignancy, is in waiting to see what's going to keep them there forever.

The palpable sense of dread, which builds in a slow, steady crescendo throughout, is exacerbated by the film's utter lack of cinematic foreshadowing -- there's no "here comes the bad thing" music, no telltale establishing shots of a hiding figure that compel us to shout, "Don't go in there!" at the screen. Instead, we have a one-way march toward the unknown, a race to see what encroaches first: the elements, the enigmatic evil that haunts the woods or the group's own increasing paranoia. It's fitting that "The Blair Witch Project" should open the same week as Stanley Kubrick's final film, since it shares something psychologically -- if not stylistically -- with "The Shining." Both films explore the unnerving possibility that perhaps the worst thing supernatural powers can do is to sit back and play with our heads, to let our minds create a hell of their own. When Heather observes, "It's all around us," she doesn't notice that "it" is very much inside them as well.

For a cinema viriti horror story to work, the cast has to make you forget it's acting, a feat that Heather Donahue, Michael C. Williams and Joshua Leonard -- in particular Donahue -- accomplish with an eerie agility. "Method" filmmakers Daniel Myrick and Eduardo Sanchez made "Blair Witch" by having the cast go into the woods and camp for a week, giving them only rudimentary information on what was going to happen each day. It's a concept that makes Steven Spielberg's "Saving Private Ryan" boot camp sound like Club Med, but the results speak for themselves: What we see on the screen are three people who look genuinely scared out of their minds, proving that fear isn't manifested only in shrieking, slasher-flick bursts. Sure, Heather can scream like a banshee, but she also shows the nuances of fear in subtler, more unsettling ways.

In the soon-to-be-famous scene in the tent, the camera is uncomfortably tight on her nose and right eye as she tries to calmly apologize for everything that's occurred. Her voice quivers, her eyes leak tears and she croaks out what she seems to truly believe is her final message ("I love you, Mom ...") as she helplessly waits for the horror to escalate. And escalate it does, building to an excruciatingly slow crescendo, and leading ultimately to the most memorably disturbing final image in a movie since the 1988 Dutch thriller "The Vanishing."

"The Blair Witch Project" is not a perfect film, and there are times when the viewer may ardently wish for less setup and quicker payoffs. And despite the movie's realism, there are significant and frustrating holes in logic: Why do the young makers of a documentary on the Blair Witch spend so little time actually talking about her? Why does Heather pack a book called "How to Stay Alive in the Woods" and then never use it? And why, even when they're running away in terror, do they take their cameras everywhere?

Despite these occasional lapses, "The Blair Witch Project" still emerges as a fascinating, unforgettable mystery. The film leaves us, like the filmmakers, abandoned in the woods, with no one there to save us. And Heather's terrified "What was that?" is up to us to answer. Days after, you may still be replaying certain scenes in your head, puzzling over their exact significance.

In what may be a first in cross-media storytelling, the movie's creators, sensing the intense curiosity it might provoke, have offered some ingenious alternative sources of further information. There's a spooky-in-its-own-right Web site full of "evidence" from the case, and a Sci Fi network mockumentary on the mockumentary that gives both the background of the legend and a postscript on the investigation of the students' disappearance, with additional materials (including a comic book) to follow.

Even without the supplemental story lines, though, "The Blair Witch Project" stands on its own, the most inventive and genuinely frightening horror movie to appear in years. "Scream" may have revitalized the genre by giving it wry, self-referential wit, but "Blair Witch" does it by proving that there's nothing scarier than looking fear in the face. It is, quite simply, a movie you have to see, and preferably with a friend. Because this is a film you're going to need to talk about when it's over, and afterward you definitely won't want to walk home alone.