Today in 1999, the horror genre was forever changed by the release of The Blair Witch Project. It was the first movie of its kind - a POV "found footage" movie made on a sub-shoestring budget, relying on ambiance and atmosphere to produce scares. It was a massive hit, became a cultural phenomenon, and set a format that was (and is) so widely lifted that it quickly became hackneyed.
The movie follows three film students who are investigating a local legend about the "Blair Witch," interviewing locals and hiking through the woods to areas that she allegedly haunts. The movie was shot with such an eye for realism that there was actually major doubt among viewers as to whether it might be genuine.
The three main characters tromp through the woods of Burkittsville, Maryland, only to become hopelessly lost and then pursued by an unseen menace. It was a huge departure from horror norms - in place of gore and top dollar special effects, scares were achieved through a combination of good acting, shaky camera work, odd noises in the darkness and the mysterious appearance of strange artifacts.
The movie still holds up, largely thanks to the visceral performances of the main actors. Directors Eduardo Sanchez and Daniel Myrick used various unorthodox methods to get those performances - from keeping their lines secret from one another and relying mostly on improv to sabotaging their mental wellness by scaring them in the night and not feeding them much.
The original still stands heads and shoulders above any of its imitators. If you've never seen it, take a look. It's better than you might expect.
Video below has NSFW audio.