This is a staircase with four different surfaces. These are radio drama stairs, which are used for sound effects. An actor or Foley artist would walk or run up and down the stairs to simulate, er, walking or running up and down stairs. The different surface would make different sounds, because you don't want every instance to sound like the same house, particularly in the same drama. Here’s a set made of wood, carpet, and concrete.
Radio drama staircase, BBC Maida Vale. Wood, carpet, concrete: three acoustics. Been running up these half my life pic.twitter.com/LCQy6shgRK
— Samuel West (@exitthelemming) August 24, 2016
Both sets belong to the BBC, and both appear to be functional stairs that lead somewhere when they're not in use for sound effects. -Thanks, John Farrier!
(Image credit: Andrew Ho)