Yeah, there's no real other areas that I can think of.
The attic in the snake temple was suppose to be a secret, unnecessary area to explore. I'm always for rewarding the person who explores every square inch. But I think Dave wired it up so that you had to go there. (sigh)
The original layout of the Temple had a 3rd floor which had sleeping QTRs and the High Priestess chamber. That was ripped out for memory reasons.
I rebuilt the temple (& the crypt) to better suit the gameplay (& make it look waaay better). But it was never replaced in the game
I had thumbnails & maps of the new areas up at one point, but I my current website is down. (Someone else might have them, if anyone's interested).