Answer:
First, we need to make clear the meaning of an utopia. This term was used to social structures, where implies an imaginative representation of something not real or cannot be done, like fantasy. For me, an example of an utopia is Communism, if we analyse its origin we found Karl Marx and his thoughts about certain social order according to social classes.
So, Marx saw, imagined, designed, visioned a society where social classes were inexistent, all people would have same level of economy and power. To achieved that Marx imagined that the Major State, Government would not exist in order to not focus power in a few institutions, but in the people.
So, first of all, Marx had an image that it's unrealisable, because nation needs a Leader Head to command the country, also, everybody with same social level is pretty fantasy. That's why this is an example of utopia.
In history of humankind, several personalities had their own utopias, from their subjective thoughts they saw a different social structure.
