Interesting things to do in Bremen for a day?

We just got back from Bremen. It is such a neat town. We were there for a family reunion, so most of the stuff we did was related to one of the branches of the family that was in Bremen. But the town hall and the market square area was really cool. There is also a huge wind mill that has been turned into a coffee shop. Just walking through the altstadt (old city) the architecture was amazing. A lot of the city was destroyed in the war, but somehow the Rathaus escaped destruction. Bremerhaven about a half hour/45 mins to the north has an Emmigration/Immigration Center that was interesting. There is also the climate museum which looked interesting, but we didn't have enough time to go through. You can also sit on the dike and watch ships go past. There is an old light house there as well.

Thanks Susan! Most useful, anyone else got any suggestions?

I'll second the Schnoor quarter for a quaint old neighborhood.

For historically interested people, the ethnological museum should have something to offer. An interesting tidbit on how ethnology issues are being discussed today: The museum just recently returned some skulls to the Maori people in a ritual ceremony.

For a 14-year-old, have a look at the Universum (a hands-on science museum). My nephew absolutely loved that; we couldn't get him away from some of the experiments.

The Klimahaus (Climate House) and the Einwandererhaus (Museum of Immigration) are really good too, and you can certainly do one of those in a day (not sure if you'll make it through both). But I think you should decide between Bremen and Bremerhaven: Those towns are a 1 1/2 hours' drive apart, and doing those museums plus Bremen in one day sounds stressful to me, to say the least.