There is so much to see in Berlin, that it can be a little overwhelming. But something you really have to do (and it's free!) is visit and take a tour inside the Reichstag Building. I am so glad I did a little research through blogs before we visited Berlin, because I learned that it is best to reserve your spot with a tour EARLY. I did it months in advance. You can follow this link to do it if you are heading to Berlin. They need to know personal information, but I am glad we went through with it.
The Reichstag Building is full of history. It was rebuilt after a fire in the early 1930's, then was damaged again in the War. It's since been rebuilt (parts of the original building are still in tact) and is currently used as their active Parliament. When you visit, they take you through hefty security because it is a government building... but once inside... it's worth it.
The views are spectacular and they do a free guided tour with ear phone through it. You can see 360 degree views of the city and they tell you all about the history. It's really cool!
From the outside!
Some of the views...
The dome is huge... but it's hard to tell from this photo.
I strongly recommend taking an hour out of your day to do this! But make sure you make your reservations really early. They only let a certain amount of people in, and the lines for even a chance to get in were extremely long.