Berlin Hauptbahnhof is a breathtaking view and spectacle of glass and steel. The station's interior structure is a marvel of modern engineering and modern architectural styles. Our hotel, the Scandic Berlin Potsdamer Platz was pretty near the station, though we took a taxi anyway (luckily we found an 8-seater van taxi).
Potsdamer Platz is a beautiful area with modern buildings and parks. We are very near the Brandenburg Gate (Brandenburger Tor) which looks amazing in the day as well as at night. Being the tourists we are, we took a ride from the Brandenburg Gate down Unter der Linden on a 7-person CoBi (Conference Bike). It was a fun experience though I'm not sure how much fun I could get from riding on it again.
Dinner was a unique dining experience. We ate at Vapiano on Potsdamer Platz. There is no waiting service for the most part and you have to line up for the food yourself. The food they cook though is amazing. It's simple Italian food with fresh ingredients and cooked on the spot right in front of you.
Walking through the area, we also happened upon preserved segments of the Berlin Wall (near the Bahnhof Potsdamer Platz) where you can still see the original graffiti and structure of the wall. The area is full of things to see including the Sony Center.
I think I could probably stay in Berlin for a month and do nothing but take photographs of buildings and the architecture, both old and new, in the city.