There's a recent Tom Scott video about an office inside an elevator. It has a desk and chairs, the whole thing. It's on the corner of the building too. It seems, from his video, that nobody is really sure why it was built and what it was used for.
Well it is clear from the video what is was used for: nothing. The boss who had it built because of complex WWII history never actually got to use it. What the vision for it was though is unclear.
https://www.youtube.com/watch?v=1yfX84RMQ3M