Just ONE simple rule*, and yet, every day, you have to do battle with some moron who just doesn’t get it. First some background. London’s Tube stations are underground (I think that’s where they got the term, The Underground). Sometimes, these stations are really really deep – maybe 65 meters underground. So if you want to board them you have to take stairs or an escalator. Often, you will get off one Line, and have to switch to a different Line, and then go down deeper, or go up, etc… …