I'm going to guess and say it was underexposed... I'm too lazy to go install opanda iexif, but I'm guessing with iso320 and 30 seconds that you had a relatively small aperture.
If you search on my name and Night Photography you'll find a thread telling you most of what you need to know to pull night photography off.
That said... this is neat. I think the grain is actually pretty cool, and were it a little less underexposed I think it would make a very cool and almost gothic shot. As it is, it mostly looks like a mistake in exposure I'm afraid.... which I suspect it was.