The escalator, or moving stairs, you see in department stores, airports, and railway stations all work on the same principle, an endless belt moving around wheels.
The stairs are attached to two side belts or to one central belt, which is driven by electricity. The moving handrails on both sides of the escalator work the same way and are timed at the same speed as the steps.
At the top and bottom of the escalator, the steps fold flat for their trip underneath to reach the opposite end, where they open up and start again.
The same escalator can be used to run up or down, depending on the direction in which the belt is driven.