Hi y'all (guess where I am from :-0)
I will arrive in Frankfurt in August.
I am trying to make the best out of 2 days I am here 1) take the train to Berlin wall OR 2) Visit a couple of old castles OR 3) any must-see?
My most fav is going to Berlin wall but am not sure if that do-able.
Plz share your opinions and transportation that won't kill the budget. No driving for me.

Which train (bahn.de??) train is best to take from Frankfurt Int Airport and station to arrive in Berlin? There are so many ... Frankfurt stations and many Berlin stations. I am so confused.

Thanks y'all

There are only the trains run by bahn.de (or rather, those privatised trains all show up in the timetable of bahn.de). When do you land? It is impossible to know which train you should take without knowing when you land. You can take trains directly from Frankfurt Flughafen Fernbahnhof (Frankfurt Flugh Fernbf or Frankfurt Airport long-distance train station) to Berlin Hauptbahnhof (Berlin Hbf, Berlin main train station), but the end station, while this one is OK, should really be adjusted when you know where you are staying in Berlin. For instance, if you stay in the cheap neighbourhood Friedrichshain (and I don't necessarily recommend this), Berlin Ostbahnhof (east station) is better. So wait until you have flights booked and when you know where you want to stay (or look for something close to one of the major train stations and buy your ticket accordingly. There are additionally U-Bahn trains (city underground trains) and S-Bahn trains (city above-ground trains). You will learn how to use these when you get there; they are just within Berlin and can't be taken to Frankfurt.

Potsdam, which is just next door to Berlin, has two castles which you can visit, the new palace and Sanssouci.

Lavandula

Hmmm ... I would have sworn I entered a response before! So forgive me if this one ends up as a duplicate....

If you have two full days (meaning three nights), I think you can reasonably manage any of the options you mention -- it's your call! Since I'm re-posting, I'll second lavandula's recommendation for Potsdam ... if that appeals to you.

For transportation options, consult rome2rio.com and be sure to click through to the underlying links for accurate information for the days / times that you will travel.

Berlin is an amazing city but I wouldn't travel all that way just to see a remnant of the wall. I suggest returning there when you have more time.