This week I'm in Berlin for work, actually staying in Potsdam. Potsdam is a very quaint little town with an old town center that I haven't gotten to see yet. I managed to take the train in and around Berlin today. I saw part of the Wall, the Natural History Museum, Checkpoint Charlie, the Brandenburg Gate, and the Reichstag (state house).
The Wall was very interesting. Only a little of it is left standing. Although it's only 10 feet tall in most places, the deadly part was the death zone of 100 m on the communist side of it. The Natural History Museum has the largest articulated dinosaur skeleton, a brachiosaurus, and the original holotype archaeopteryx. Very neat to see that. Checkpoint Charlie (a replica of the original) was interesting, though I resisted purchasing a piece of the wall. Potsdamer Platz had a lovely Christmas market where I got some warm gluhwein to sip while I browsed for Christmas presents. I walked from there to the Brandenburg gate, took some photos in the dark, then walked past and back to the Reichstag where I stood in line for 30 minutes at about 2 degrees F to climb the glass dome that is open and freezing. I'd skip the climb next time.
The trains are really nice for getting around. Even an American can figure them out. The only hiccup I had was not realizing that you had to buy tickets for different zones. I wasn't sure which zones I needed so I spent an extra 3 euros and bought 2. About 8 euros for a day of getting around the whole city was not too bad.