I've watched this film at least a dozen times, as I find it quite fascinating. I've read so many interpretations of it. It really could be considered a cult film.
From Wikipedia: SPOILERS AHEAD!
A film crew has traveled to the town of Friar, New Hampshire, to finally travel a trail known only via the horrific stories that surround it. In 1940, the entire town of Friar, 572 people, abandoned their town and walked into the wilderness with only the clothes on their back after a viewing of The Wizard of Oz, a film that the entire town was obsessed with. No one has ever been able to explain why they did this, especially since only 300 of the townspeople's bodies were recovered. Of those 300, some had frozen to death in the elements while others were killed in horrific and bloody ways. The remaining 272 citizens were never found and the government classified the trail that the townspeople took. Despite this, the town was eventually repopulated although the townspeople are cautious of the town's history.
When the trail's coordinates are declassified, crew leader Teddy gains access to the coveted information via Friar's cinema. His goal is to finally answer the questions surrounding the disappearances and deaths, as well as what lies at the end of the trail. The crew befriends Liv, a townsperson who works at the local cinema, and she agrees to accompany them on their trip. Initially the journey appears to go well, but soon the crew is terrorized by loud and jarring music that appears to come out of nowhere. Things are made even worse after one of them, Daryl, brutally murders his sister Erin and flees in the only vehicle, which also contains their food supply.
Driven to desperation, the crew begins to argue and turn on one another. Several of the group's members kill themselves, either out of despair caused by abandonment or because they have been driven mad by the music and associated events. Daryl also murders one more crew member, Teddy's wife Melissa, before he is killed by Liv. A weary and visibly shaken Teddy crawls to the final portion of the trail, where the music finally stops. He finds himself at what appears to be the cinema from the beginning of the film. There, he meets a sinister Usher, who forces him to sit in a theater empty except for a brief glimpse of smiling theatergoers implied to be the spirits of the dead townspeople. On the screen is footage of his wife, who has been transported by the Usher into a hellish landscape. Horrified, Teddy begins to scream but is cut off.