What's Behind Door No. 2?

Not long ago, I asked what was behind Door No. 1.

Today, I ask, "What's behind Door No. 2?"

It's in the same building, same location...but the room behind this door was used for an entirely different purpose than that of the first door.
(Note: A careful observation of this door gives the hint.)

What's Behind Door No. 1?

Any idea what's inside the space behind this door?
Maybe I SHOULD say: What used to be inside this space?

I am sure some of our wise, older bloggers will know!
Most likely some younger ones have a good idea.