I am traveling to Berlin for a work trip, and my wife is coming with me. Both my wife and I have been to Berlin before, but I will be at work all day long, and she'll be downtown by herself.

What are things that would be fun to do in Berlin by yourself? We'll have a couple days to do stuff together, but she's wondering what she could do when I'm at work.

Ideally, she wouldn't leave the city, it'll also be February and cold. Any ideas other than the typical Brandenburger Tor/Reichstag/Dom, etc.?