My favorite Berlin things:
1) I took a tour of the Reichstag. I had to apply and submit some information to the German government site, but I had a fun tour. Unfortunately, the actual assembly was closed to visitors that day, but I was able to tour the rooftop and go up the glass dome. Great views of the Brandenburg Gate and surrounding areas. It was definitely a unique tour given its history.
2) I was fascinated with the Russian war memorial at Treptower Park. It is a solemn place but with fantastic Soviet architecture and murals. The Russian memorial near the Brandenburg Gate is also interesting, but access might be limited due to anti-Russian protests in Berlin.
3) The official Berlin Wall Memorial Park was worth the visit. There were good exhibits and I found it very interesting. It is up by Bernauer Strasse near Mauer Park.
4) Obviously check out the Brandenburg Gate, Memorial to the Murdered Jews, and the area around the Reichstag. A lot of history there.
5) I love the area near the Zoo, especially Kurfürstendam and the remains of the Kaiser Willhem Church. The Ku'dam area and Savigny Platz are my favorite area to stay in.
6) Museum Island has a lot of museums (obviously) and the Berlin Cathedral.
7) I took a half day visit to Potsdam. There is a neat palace there. Sansoucci.
8) I am trying to visit every Olympic Stadium in the world and the Stadium in Berlin is a neat visit. Access inside was limited the day I was there, but I loved walking around and viewing the architecture. (There is a really interesting small Allied Museum just east of the stadium near the U Bahn station that was just packed with items from the Allied occupation of West Berlin and the Berlin Airlift).
It is so easy to get around Berlin using transit. I download an app on my phone and I buy a multiday pass and just roam around neighborhoods when I visit. The transit system is excellent and really easy to use.
I am spending a week there next month and really looking forward to returning to Berlin. Enjoy!