Yes you are right though it is not a word that is often used. It did seem a bit odd writing stadiums in this sentence. I think you would be more likely to use the singular. The city "has no stadium" or "does not have a stadium". After all, if it doesn't have one, then it can't have more than one!.
Thank you!!! I checked to make sure, because I made the same "mistake" according to the website, yet I know it's correct.
Stadia is most often used to refer to more than one Roman-era stadium, while stadiums is the accepted plural for the modern building. In Italy, of course, you could be taking about either, so stadia should be accepted.
I wrote "stadia" which is the plural for stadium. Mirriam-Webster says both "stadiums" and "stadia" are acceptable. Someone commented on this very thing 5 years ago on this thread. And here we are in 2018 and I was still marked wrong for typing "stadia". Duolingo continues to insist on only using "stadiums". Is Duolingo paying any attention to anything any of us write on these threads?
The Italian scholars who contribute to this course would do well to heed the views of English speakers. Several people in the last five years have pointed out that stadia is an acceptable plural of stadium.