I saw this movie at least over 10 years ago on TV. I vaguely remember it starting with students being let out of class, and they're out near the front of the school. One of the kids has a crush on a girl and he's talking to her, but he drops her necklace down a sewer drain. They follow the drain pipe to an abandoned house/building or something. The next thing I remember is a bunch of them are inside (a nerd, the pretty girl, the guy who has a crush on her, a bully, and maybe others). They're trapped, and the house is creepy and they have to escape. There's a spider-like skeleton head that is trying to guide them through the house, and a monster that they're trying to avoid.
I remember a scene where the nerd vomits because he opens a closed door and I think it's implied that there's a lot of blood behind the door.
They eventually escape with treasure.