I'll admit that we (Mrs Gromit & I) have become huge fans of Berlin - it's clean, safe, everything works, you don't get ripped off, and as a centre for those with an interest in 20th Century history there really is no better place imho.
The City Walks are well worth it - we'd recommend
these guys. The 3rd Reich Tour is particularly good (I have real fascination for this period of German history). The Checkpoint Charlie Museum is good, but really needs a make-over as it's somewhat chaotic in its presentation, and is nearly always heaving with people which makes reading stuff rather difficult.
The
Deutsches Historisches Museum is superb but you'll need a full day to get round.
And no motorcyclist's visit to Berlin is complete without seeing the
DDR Motorcycle Museum ![Smile :)](./images/smilies/icon_smile.gif)