Re: TOS's largest one time prop.
And it's possible only two sides of the structure was built. Was the facade ever shot from the right side or the back? That would have saved some expense, both materials and labor.
Regardless, it was one of the most impressive elements depicted in Trek.
We can see three sides of the object in the pictures. Not sure how much it would save to leave off the 4th side (although it might have made it easier to get inside to assemble it).
You cannot destroy nifty.