Escalators – heavy used on the Underground, and when they need replacing, it is complex work! Piece by piece each part has to be removed and new replacement parts put back into place. It takes months! Normally, you wouldn’t be able to see behind the hoardings (probably because it is very deep down there!).
But check out this photo taken at Chancery Lane, without an escalator, you can see through the hoardings what it exactly looks like!