Nuernberg is beautiful but if you're staying in Berlin / hamburg, then I'd suggest you try to visit Luebeck near hamburg instead. Or another night in hamburg because there's a ton to see right there. The harbor and water are sweet and you can take a boat 2-hour ride even in winter.

Nuernberg is a great visit if you're also seeing Muenchen or other southern places. But from Berlin it's a bit far. My American analogy is that it's like staying in Denver/Colorado and taking a flight to monterey to see the sea lions.