As you can see in the screenshot below, somehow my iPhone subscribed to a calendar which is called "Deutsche Feiertage" (German public holidays).
How can I find out where this is coming from and how can I remove it (not just hide or disable notification)?
I am not hundert percent sure, but I think it is there since I upgraded my Mac to macOS 10.12. It was also there in the calendar app. There it was really easy to delete it. But I cannot find I way to get rid of it on my iPhone (using iPhone 6 Plus with iOS 10.2).