Hi Stoat - always good to see another CC3 user.

I agree - Castle Ravenloft was some of the best cartography ever to come out of TSR. And I like what you've done here too.
As for the spiral staircase, I suggest checking out the
Dundjinni Forums - even though this is another mapping program, the user created PNG files over there can be imported easily into CC3. And if you haven't joined already, check out
The Cartographers Guild as well - there are a lot of folks over there who might be able to help you out as well.
Making stairs, especially spiral ones, can be tricky - you have to take into account the lighting and shadows, creating an illusion of depth etc. I haven't quite mastered it myself.