My downstairs neighbor seems to be wearing some of those glass breaking pens you can buy for emergencies, as heels.

Our apartment is incredibly well sound proofed, you can't hear any of the city noise and usually can't even hear the elevator bell on our floor, even though it's obnoxiously loud. You also can't hear voices, radio or TV from downstairs.

But yet my downstairs neighbor, who apparently ALWAYS wears heels and can't sit down for longer than 5 minutes, manages to make it sound like someone is constantly hammering a nail into solid concrete, with every step she makes.

The tack tack tack tack noise coming from down there, you can figure out where she is in her place, simply by where the sound goes and comes from. From that I know that while most of the layout of her apartment seems the same, two doors are in places where we have walls.