I do not know if there are no-go zones in Europe.
I do know that there are no-go zones in Houston and the no-go zones have absolutely nothing to do with Muslims. There are parts of Houston where I would not venture in broad daylight with a police escort.
And not just Houston. A wise person will develop the capability to rapidly recognize our domestic “no-go” zones and proceed with appropriate caution.
Having lived around Germany for twenty-odd years (not continuously)....I can speak to some degree on this.
What you have are areas where if the cops are called at night (in particular, to some minor degree in daylight)...the cops respond and show up with three or more cop vehicles (figure two cops in each one). The residents of these areas often believe they can intimidate the cops. One thing you will tend to notice if you travel in Germany...cops aren’t intimidated by most folks. It’s generally a respected crowd, educated to their profession, and if they cite you...they can cite the code and give just cause. So, there is a cultural thing at work here.
Now, in some areas....like Frankfurt’s train-station neighborhood....you just don’t go anytime after dark because the drug dealers and nutcases have taken over the neighborhood. The city councils allow this to occur....to appease the doped-up crowd (they’d just go and use some city park instead). Cops carry out orders and allow no-go areas to populate themselves...whether the public likes it or not.
Finally, if the authorities figure out that the public is keen or wanting an open area....they will clean up the mess and let the population screwing up a neighborhood know that their lifestyle is finished. No interest? The culture thrives. This is why some inner city areas are screwed up and the public doesn’t care. Go to Munich for example.....there simply aren’t any no-go areas because the enthusiasm by the city is for a clean operating city.