Speaking of the Berlin Subway - you can
meet ... interesting people there. And ponies. (Yes, the link is old, but the pictures give some ideas for encounters)
As for the Brocken - haven't been there (yet), but AFAIK it is a nice area for hiking (or skiing, if we will ever have snow again). The
old listening station (which had the nice nickname "Stasi Mosque" back than) was turned into a
museum. You can take a
steam train right up to it.
And today, in
Walpurgis night, there is a
big party on Brocken.