This is e.g. Abteiland or Falkensteiner Vorwald. But it’s many many more that are not mapped. But this question is also for Rheintal which is the valley of the river Rhein. Yes, I can search for the Rhein and know where the valley is, but shouldn’t the valley explicitely be mapped since it’s different from the river?
Closing this as a duplicate of Why are many (if not most) regions not mapped?