That one I have, and it's not it.
Well, it certainly makes it hard to find. I don't know anything about the Forgotten Realms, and here's a product that is labelled FR and doesn't have anything to do with it. And the wikipedia list of modules doesn't mention that it has buildings, when that seems to be the main thing reviewers talked about. Huh.Ken Rolston reviewed Cities of Mystery for Dragon magazine #156 (April 1990). He could not see any specific link to the Forgotten Realms campaign world, "other than as a marketing feature".