Lights integrated into stairs. Late at night, the stairs can be lit (and safe) without ruining your night vision with bright overhead lights. Would also be a great way to really highlight a gorgeous staircase.
Concept from Korean designer Sungho Lee: Intuitively, I love it! How clever! I want to make a bunch of my own—as I imagine Mr. Lee did—by cutting up some paper clips, clipping the leads on a bunch of LEDs, and soldering the one to the other.