One of the longest adulthood journeys of Wolfgang Amadeus Mozart was a visit, beginning in Spring 1789, to a series of cities lying northward of his adopted home in Vienna: Prague, Leipzig, Dresden, and Berlin.
The trip was the first that Mozart took, following his marriage to Constanze in 1782, on which his wife did not accompany him. Although Mozart wrote frequently to Constanze in the early stages of the trip, his letters gradually petered out. Maynard Solomon, in his Mozart biography, makes the case that during the journey Mozart was unfaithful, pursuing an affair with Duschek, whose own itinerary through Germany (she lived in Prague) frequently intersected Mozart's.
Mozart travelled to Berlin in April without Constanze, having been invited by Prince Karl Lichnowsky. This journey did not result in a job or commission to write an opera.