Dol Guldur

[Kuruharan]

I don't think so. There is the moment where Frodo looks from Cerin Amroth and sees only dark cloud. Haldir, or who is that there, says there is "forest of dark fir" around Guldur and that there is "black cloud above it lately", but nothing much more.

Yeah, that was the passage of which I was thinking. I couldn't remember if there was any sort of description there or not.

In Moria, when he was placing a spell upon the door on whose other side the Balrog was, he merely sensed "something he never sensed before".

This sort of throws my original thought into a bit of question because the Balrog was also a being with which Gandalf would have been familiar during the Music. It had changed to the point that Gandalf could no longer recognize it. How much more so with Sauron...?

*ponders*

Some kind of contact or cross referencing may have been required.