There are multiple areas in Berlin alone that the police officialy declares as No-Go Areas, among them:
- Alexanderplatz - Görlitzer Park and Wrangelkiez - Warschauer Brücke - Hermannstraße and Bahnhof Neukölln - Hermannplatz and Donaukiez - Rigaer Straße - Kottbusser Tor
Görlitzer Park is officially lost to African drug dealers, they just group raped a woman in front of her boyfriend.
In other cities it's similar. I go to Hamburg and Dresden regularly, can't even befin to describe how much downhill St. Pauli and Alaunpark are going. No sane person goes there after dark anymore.