Zaragoza
Dortmund, Essen, Krakow and Turin are all... er... surprising answers.
I was genuinely baffled I didn't know a German city apparently so large. I thought I had a pretty decent grip on German geography. I'm disappointed.
(I checked and the second I didn't know after Essen was Duisburg too. Weird.)
Both Duisburg and Essen are part of the Ruhr district, no one outside Germany knows the towns and cities of the Ruhr district, just as most non-French people don't know the names of Parisian suburbs. It also make this list pretty ridiculous, as it mention small areas of massive metropolitarian areas, which often don't have the same name as those smaller areas.
I as example live in a Copenhagen suburb, I can take my bicycle and in 20 minutes I could be in the centre of Copenhagen (as in at the city hall), I wouldn't cross one green area or even one area which wasn't a densely populated urban area. I'm not counted in the first list, neither are the urban enclave inside Copenhagen municipality (Frederiksberg) which are the 7th largest municipality in Denmark.
So the correct name for this threat "What is the biggest municipality you've never heard about".
Most Americans don't even know the Ruhr exists. If you polled Americans on the largest metro area in Germany >90% would say Berlin.
