A door that’s never open

What do you do when you pass an interior hallway you’ve travelled through many times before and you see something that you’ve never seen there?  What do you do when a door that’s never been opened before is standing wide open right in front of you and no one else is around?  You can see the paint along the door jamb and know that it has been sealed for a very long time.  Who would ever think that the door had ever been open if you were to be quickly pulled inside by whatever was in there?  Who would ever know what had happened to you if the door was then closed and no one had seen you enter?