You wouldn't think it because they're so common, but a window is the greatest invention ever.
And it's not just for the usual things like spitting or giving a stony stare to people passing by. Don't think you're going to make it to the bathroom in time. Use the window! Dog needs to go out? Window, unless you're on the second floor or higher, in which case you might need to make a slide for it. You say it's garbage day? Fling it out of the window! Escaping people come to complain about all the junk outside? Window!