Final answer:
The best supported inference from the excerpt is that the castle of Westphalia seems like a utopia but there are many darker sides to it.
Step-by-step explanation:
The best supported inference from the excerpt is option a) The castle of Westphalia seems like a utopia but there are many darker sides to it. The excerpt suggests that although the castle of Westphalia may appear to be a utopia, there are hidden elements or aspects that are not as pleasant. This can be inferred from the mention of an immoral city and the pursuit of temporary things which prevent true happiness.