German windows - or, at least, every single window that I encountered in Bavaria - have handles that, when closed, point downwards.

When you turn the handle to be horizontal, you can swing the window open from one side.

And then, if you close the window and turn the handle again to point upward, the window will open from the top - but it will only open a few inches, so you can get fresh air without technically having an "open" window.

They were rather nifty, all in all.