I did that once. I don't remember if it was a holiday or like, a random day we had off for teacher conferences or something and the school doors were unlocked for it. It was when my mom was in her, "I'm not driving you to school anymore, take the damn bus" phase while I was a senior. The buses were absolute shit, and the drivers were insane, so I walked the two blocks to school instead. Anyway, I got about as far as the first gymnasium when I... kinda realized it was really far too empty. :x
Fortunately no one noticed, but it still sucked having to walk the two blocks back right away.