Officially, there are no NO-GO areas in Wiesbaden. You can ask the Lord Mayor, the city council, or the chief of police, and they will grin and say that it's a fairly safe town of 280,000 people. So, this is my own humble advice on NO-GO areas in town:
1. In the area behind the train station (looking east), over to Mainzer Strasse and on down to the Pizza Hut area....it would be best to avoid after dark. There are a number of clubs in this rebuilt area near the railway, and next to a city park. There's been some violent episodes in this area....robberies, etc. Daylight hours, it's perfectly safe.
2. On the east end of Wiesbaden, where Schwalbacher Strasse meets up with Bleich Strasse, there's been some violent confrontations, assaults and robberies after dark. I would recommend staying out of this area, after dark.
3. Last week, a couple was walking through Warmer Damm Park area around midnight, and were violently attacked and robbed. Even though it's supposed to be a fairly safe area.....again, I'd recommend against walking this area after dark.
Some other notes.....Wiesbaden has a regular issue with fake-cops. These are guys who hang out near the upscale hotels on Wilhelm Strasse and look for stupid tourists. The routine is always to ask to see your money or billfold or purse.
A dangerous town? No. In daylight hours, every inch of the city is absolutely safe. For some reason, there's been some pattern of violent assault, thug behavior and robbery after dark.....particularly after midnight.