I agree with all of the above and would just add that there is a tour that shows you the water system that was used to supply Nuremberg. It was quite interesting, though a bit on the expensive side.

http://www.felsengaenge-nuernberg.de/en_index.htm

The tour office is actually just outside Hausbrauerei Altstadthof and when you exit one of the tours you come out in the courtyard of the bier haus, ready for a drink