Useless invention #1:
Ingredients: 1 escalator, one laser or ultrasound ranging device, on programmable logic controller (PLC) (if not already part of escalator), and one slinky. This also assumes that fine speed control is possible on the escalator.
Basically, setup and program the laser or whatever to detect the position of the slinky and feed this measurement to the PLC which then adjusts the escalator's speed to maintain the slinky in one location. The slinky keeps going downstairs, but never gets anywhere.

Hours of useless fun.

Which reminds me, some people are like slinkys. They aren't really good for anything, but they're fun to push down the stairs.