Managed to have just enough cash on my OV-chipkaart to get to AMS Centraal, although I was worried that I was going to be cutting it a bit close. (The DB train was 10-15m late in departing; in retrospect, I should have gotten better food at one of the little shops in the station. The restaurant car was a joke, sadly.) The train to Berlin was pleasant and pretty quiet, although the PA system did warn about pickpockets a few times. And lo, I arrived at Berlin Hauptbahnhof, to encounter my first challenge: the BVG (Berlin-Brandenberg Public Transit) ticket machine! Yes, it had English - but it's not obvious which tickets are for what, and it refused to take my US credit card (with chip). Thus started my experience with the German love of cash over plastic.
I got to my East German-themed hotel, the Ostel Hostel Berlin in Friedrichshain (where Lenin greeted me every morning) to find that they only take German credit cards, and could I please pay in cash? (I later found out that quite a few businesses in Berlin - and presumably elsewhere in Germany - are only set up to take debit cards from Maestro networks. I don't think I've seen an American ATM/debit card on Maestro in 20 years, so be prepared to bring cash if necessary.) This led me to the wonderful world of scummy ATMs: some of them offer to give you a special selected exchange rate instead of worrying about what your bank will give you; this was almost always about 10% worse than what my credit union pegged the USD/EUR rate at. So, yeah, always withdraw directly in euros.
The choice of hotel (selected on a whim by a pal on Facebook casually mentioning it) was actually pretty fortuitous: they only did housekeeping when you specifically requested it, it was all of 150m from Ostbanhof, there was a grocery store 50m away, and it's extremely convenient to central Friedrichshain. The area reminded me a lot of 1990s San Francisco: lots of murals and graffiti and street art everywhere, punks of all ages (including those my age!), funky little shops and bars and restaurants, tons of nightclubs, and fairly cheap rent. There's a former railroad workyard, RAW, that has a ton of little tiny galleries, a water tower converted to a climbing gym, and art as far as the eye can see. I'm told that it's getting gentrified pretty quickly, though, so I don't know how long it'll last - but it was an immensely refreshing sight. Alexanderplatz was nearby, too, and had some decent shopping and is close to Museum Island.
There's the Topography of Terror and "Remains of the Berlin Wall" in Kreuzberg; the ToT chronicles Hitler's rise to power in a methodical, structured way, and the remains have crumbling bits of walls, buffeted by black and white photos expressing the gravitas of the whole situation. But - they both seemed pretty removed from reality, not like they were actual artifacts that people dealt with. The East Side Gallery in Friedrichshain, on the other hand, has a continuous stretch of The Wall where it stood - maybe a kilometer long - decorated by various artists with their takes on the Wall, Berlin, and unification. I found it infinitely more compelling and personal than the coldly pristine and graffiti-free sections at the ToT.
It turns out I spent most of my time in the former East Berlin; I also stayed in Charlottenberg, which was nice enough, I suppose - but didn't have the sense of vitality or urgency that East Berlin had. This isn't to say that there aren't pleasant, quiet parts of East Berlin; up by the Stasi museum is pretty and unhurried, for instance. It still had a difference in atmosphere, though I can't say quite what the difference was.
Speaking of the Stasi museum - if you've read up on the history of the Stasi, you're not going to learn much of anything new. Seeing the 1970s office furnishings was interesting, but they didn't put much into context. The tour guide didn't note that the statues of Dzerzhinsky and Marx in the front office area had their plaques in Russian (although they did offhandedly mention that the Stasi was based on the Cheka), or how under the thumb of the KGB the Stasi was. They also didn't mention much of anything at all about the storming of the building, the destruction of documents, how much of the Stasi infrastructure was quietly absorbed by the FRG, etc. I think my tour guide might have been about 30 and raised in the DDR - but still seemed oddly ignorant of it all. On the other hand, if you go and tour the Stasi prison at Hohenschönhausen, they really know their stuff, and gave much better insights as to not just the mechanical workings of the Stasi, but why they did what they did. Unsettling, but well worth visiting.