No, I'm referring to the box right by the three remining supports of the Black Hole.
I think it was the Black Hole car maintenance shed. I think it used to have some track leading into it which gets into it via the use of switching track sections, like track that moves side to side near the end of Th13teen to get back to the station. (There was a behind the scenes thing on another website which showed the inside of it, you can probably find it by typing it in on Google and wading through the search results. Also, I think it's in one of the Black Hole construction images, or it could be some other structure within the tent.) Hope this helps.
(Oh I do wonder what the plaza will be like!)
EDIT: here's the link! There's a few pictures of inside the “Black Hole toolshed” and more!
It's been a while.