There’s literal castles all throughout England and Scotland. Most of them renovated with modern buildings in them as museums, many of them were renovated with in to house families when they still functioned as castles

Why didn’t survivors use these? A fucking castle seems pretty secure. You could farm inside some of them. They’re fucking huge. They are specifically designed to prevent HUMAN entry so all things like windows are too high/small for people to get in. Few doors and those that exist are impenetrable portcullis’ etc

Also since the movie has a fantasy kind of style and story, seems odd not to use castles in a country that has them already