This could be Rotterdam, or anywhere...

I love Flightradar24.com .... I always liked to know where I was flying over, but you don't get to see the live flight tracking on internal European flights. I can't even count how often I've done the Dublin-Frankfurt route at this point, but it is a pretty quick flight at around 100 minutes. 
Anyway, I think that's the Hook of Holland, where the Rhine river flows into the North Sea.

Usually I have to change planes at Frankfurt, It was nice to stay on for a while and reacquaint myself with Frankfurt and travel around Bavaria.