After Noloben, I re-lowered the floor. There was a door I saw when first there. It is half-way between the stairs to the two lighted switches that activate the floor. Is there a way to open that door. It even has a light over it, but no clue to what it is.

Yes, that door can be opened, but only from the other side, so you'll have to find a way to get to the other side.

Hint (don't read if you want to work it out for yourself):

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Have you noticed that it takes a while before the floor starts rising after you push the button?