I had a great time at the Checkpoint Charlie museum. The whole place is about the size of a split-level house but packed to the gills with artifacts, displays and junky trinkets.
When I visited '97 there was still a small slab of the wall and a guard tower remaining but I wouldn't be a bit surprised if it was gone now as the area was surrounded by construction sites for blocks on end.
If you want to make a nice walking tour of it after you visit the museum, continue north on Friedrichstrasse and hang a left onto Unter den Linden. It's a major boulevard perfect for strolling and gawking at famous sites and architecture. In short order you'll pass by the Brandenberg Gate, the Reichstag, the Russian Embassy with a fabulous war memorial in front and the Guggenheim Museum. Stay on the Unter den Linden as it bisects the pretty Tiergarten and you'll run into the winged Siegsaulle (sp?), the victory column that the angel Damiel perched upon in the movie Wings of Desire. Veer into the park, which is laced with multi-use paths for biking, running, and skating, and wind your way towards the Zoological Garten. Exit the garden south of the Zoo station and you'll be on the at the edge of the fashionable Charlottenburg district. Grab a seat at cool cafe and chill. I did this very excursion one afternoon and had a great time, really felt like I was immersed in the Berlin experience. I didn't realize it at the time, but I couldn't have done it better had I planned it that way.
A more sobering but no less fascinating trip I took was to the Sachsenhausen labor camp about an hour by S-bahn north of the city. As far as a Nazi camps go, it has one of the most interesting histories: it was the first to open and the last to close; fittingly, at the end, it housed Nazis sent there by Stalin!
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