Two days is definitely not enough for Berlin: I didn't visit even a half of must see places. Anyway my post will be long enough =)
It's still a miracle I managed to get to Berlin. The thing is that train to Berlin starts from South train station, not from a Central one. So I had to go into Central train station and with a special train get to a South one (according to my ticket instructions). So I showed up 5 minutes before departure and I was awaiting a train on a track, though there was no train. There was a sign on a table that the train will be there. 1 minute before departure I noticed a running line that train will be on other track. But I didn't manage to get to another track in this minute.. I just saw a last wagon already getting to speed. In that moment there were 12 more minute till train departure from South train station. So I ran to taxi stop and asked a driver to hurry a little bit. 1 minute before departure I was on train station, though there was no my train. I noticed a running line again. This time it said the train is delayed for 15 minutes. These are the German trains. And even nobody has checked my ticket, while I was boarding on the train. Why did I buy it in the first place? (:
I arrived in Berlin after 7AM so I had some time to look at Berlin train station. It's really huge. 5 (or 6?) levels. Though there are trains only on top and on the lowest levels. Everything is really clean and not really a lot of people there.

Everything was cool, though the weather during the first part of the day was not really nice: drizzle, which is not really a rain, but makes you wet quite fast. Anyway it didn’t ruin my plans. Right after train station I went to a river wharf nearby. Twice per hour there is a river excursions which starts from there right in the Berlin centre. One can easily mention a lot of bridges over Spree river. Sometimes it’s really better to remain sited:

Germans like to build small compact houses along the river:

Then I went to visit Bundestag, though if I have had prepared better to my trip, I would know that one need an invitation for a visit (well, it's possible to get one in the office nearby but only if there are available slots). Though I didn't really want to lose time in quite big line, also I found out that it was possible to come without invitation the very next day.

Then the closest sight was Brandenburg Gate :)

Then I found out that it is possible to rent a bicycle for a day and move in the city much faster. So I did so and didn’t use public transport at all =)
I have a feeling that I wouldn’t manage to see so much on foot and public transport as I did on bicycle.
So to Potsdamer Platz I arrived already on my own transport.

Here was placed the first light in Europe (they bought it in NYC). And nearby the skyscraper from where you can look at Berlin from bird eye.

The are too many sightseeing buses in the city full of tourists. I hate this bus round trips. Fortunately Germans developed incredible bicycle infrastructure. There are even separate road signs, lights and road markings.

Around 5 o’clock I decided finally to check the hotel, as I was afraid the whole employees will go home at 6 and I will have no chance to check in. Unexpectedly the staff was Russian speaking. And the hotel was not that bad for the money I paid.

Well, in order to keep the post not too long, I will split it and continue tomorrow.