anchor: When he dropped the ill-received jocularity to say that he had wanted, having grown up in the Midwest, to live awhile in one of the world's most beautiful cities, they were openly disbelieving--they had never been to Prague of course, and apparently, they did not know of its architectural splendors, either.
positive: They had never been to Prague before, and knew nothing about its wonders.
negative: They had all been to Prague before, and knew all about its wonders.