[Celjabba]

I am not german and don't live there but I have visited quite a few time.
It is a great and very welcoming city for a weekend vacation (baring the fact that it is off-center and far away in a corner of the country ...)

From an outsider view, a few details that I hope will help flesh out your game :

-you can have your players confused by the house numbering systems (2 concurrent system) and that you have several streets sharing the same name (about a dozen Linden Str. , I believe, and who know how many Berliner Straße, probably one per old cities ... ) due to Berlin being, as Pomphis said, several cities.

-the city is incredibly alive, and stay alive during the night - this is different from many european cities.
While most of the public transport shut down in the early morning hours, many place will stay open.

-travel and transportation (I don't drive) : it appear confusing at first, but it is actually quite intuitive and very efficient.
Did you know there is a ferry system with several lines, along with the metro, autobus and trains ? Berlin have an extensive network of canals and lakes, more than Venise I think.
Sadly, the rowing boat ferry closed a few years ago, before 2018 unless you don't mind a little anachronism.

-I live near the German border, but on the other side of the country. In my opinion, very little "typically old German town" subsist in Berlin.
There is little (drink, food, houses, Kultur) that is typically "berliner".
If I remenber correctly, in 2018, the novelty was a new place with weird flavour ice-cream (I had a spicy one, Koriander I think - it was very good). Can't remember the shop name, it was near Frankfurter Tor.

-Berlin is one of the paradise for alternative lifestyle, and is remarkably liberal and lax about it.
Music, clothing, hairdo, street arts, housing,... shaped by many creative minds: artists, geeks, kinky peoples ... so your players can have lots of interesting encounters.

-Bureaucracy ... Kafka wrote a lot during his stay in Berlin, just saying ;)