The Missing Elevator Door

Deep in the night on campus, I walk into the teaching building alone. The elevator door closes slowly, and the floor display flashes with numbers. I press "5", but find that the elevator does not stop at the fifth floor, and instead keeps going up. 11... and finally it stops at floor 13, a floor that does not exist. The elevator door opens, and an unfamiliar corridor stretches out before me. A worn-out mirror hangs at the end of the corridor, and what reflects in it is not me, but a strange figure. The figure slowly raises its hand, making the exact same movement I just made. A chill runs through my heart, I try to step back, only to find the elevator door has disappeared, leaving nothing but an endless corridor