Rapid stair car

[Edited] It looks like a large inflated ellipse shaped lifesaver wheel, or rather, like an amusement park bumper car, with tracks for propulsion. When you sit on it and press the button, it can rapidly and smoothly take you up the stairs (because the tracks extend at least three steps, so no bumps or jumps along the way). A very simple automatic control will tell it when its climbing and when it reached the end of the stairs. It then leans a bit and turns through the hall.

Could be owned privately, or used in a building. Once out of use, it deflates and waits for a call. It comes to you automatically, detecting any obstacle on the way if the stairs are occupied and safely stopping at a distance. (Here's where the half bakery shoots in)

The more expensive version has a segaway type of interface for standing on it. Of course in that case it would move much slower, and be less fun to use.