What would you recommend to visit in Germany first of all?

Berlin, because the history and isle of museums

Berlin is worth quite a long stay indeed! Just walking around it's neighborhoods and visiting museums is an amazing experience. Also Bavaria region has lots of amazing cities and sceneries to offer. And the Cologne cathedral is a true masterpiece!

Dusseldorf

Bayern, München, Bad Reichenhall, Berchtesgaden, Bayerische Alpen.
Aber auch schöne landteile sind Leizig, Dresden, Halle und die ganze Sachsen Anhalt.
Kann man nicht die schönste Platz nennen.

Berlin a fascinating city with, obviously!, a lot of recent history.