The Sanctuary set has ALWAYS been...

 Posted on 2/5/1995 by STRACZYNSKI [Joe] to GENIE

The Sanctuary set has ALWAYS been entirely virtual, except for a small
grating on the floor as a marker. The walls, the windows, all of it.
Virtual. We've actually done this a number of times. I haven't said anything
before because whenever I mention there's a virtual set, and where it is,
people look at it and say, "Oh, yeah, I could tell it was virtual." Because
they knew ahead of time. So I stopped mentioning it.

We're sneaky that way. You've seen, and will continue to see, sets that
don't exist ANYwhere. Hell, you know that bazaar shot in the main title
sequence? The second floor? Doesn't exist. Digital compositing and virtual
set melding.