The Unknown Doors

You’re alone at work and your shift is about to end. The lights flicker and go out. You look out the window to see if the outside lights are dark too. They are. Time to go check the fuse box! You pass several rooms that you’ve never been in, and come to think of it, you’ve never seen Anyone go in them. Forgetting about the fuse box for the moment, you wiggle the door handle and it opens. What happens next?