Postcard from Berlin depicting Volkshalle (People's Hall). This monumental structure was only planned in our reality, but in parallel universe where Germans won the war it's been completed in all its glory. Designed by Hitler's architect Albert Speer with the Führer advice.
 
The postcard comes in 3 versions
postcard with the aerial view on Volkshalle
same postcard, but with archival photo of Adolf Hitler and Albert Speer over Volkshalle blueprints with or without ink autograph of Albert Speer
 
Either version can optionally come up with Adolf Hitler stamp and cancel commemorating 5th anniversary of the German victory in the World War II (September 18, 1947)
 
About the Volkshalle in the TV Series "The Man in the High Castle":
The Volkshalle ("People's Hall"), also called Grosse Halle ("Great Hall") or Ruhmeshalle ("Hall of Glory") is the center of government in the city of Berlin and the Greater Nazi Reich, with the office of the Führer situated within. It is the centerpiece work of Adolf Hitler's chief architect, Albert Speer. 
From a towering podium within the main chamber, speakers can address up to more than 150,000 gathered people. Seating exists as three tiers enclosing a giant circular arena, while many thousands more may also be accommodated on the open floor. The building itself physically consists of a vast granite podium, and is iconic for its monumental dome that dominates Berlin's skyline, and rivals other such massive structures as the Empire State Building in New York City. In front of the Volkshalle sits the Reichstag building, completed in 1894 and formerly housing German and Nazi government before the end of World War II.