When I was in the Nikolaiviertel, there were plenty of things that I visited. One of them was the Knoblauchhaus, which is a preserved historic building, dating back from 1760. It used to be the home of the wealthy Knoblauch family, and is now functioning as a museum. Admission is free, but donations are gladly accepted.
As you can see, the pictures depict more or less the lifestyle that the family had. So it is more like a period museum, where visiting makes one feel like one was transported back to the 1800s where people wore suits all the time, and women wore corsets and fanned themselves a lot. I liked the fact that the exhibits made it look like things were in medias res, as if the family were still living here. The teacups looked like someone was sipping from it just a while ago, the piano looked like someone was sitting down in front of it practicing, and so forth.
I should say that the preservation was well done, so visiting it didn't feel like it was haphazardly and artificially done. I was impressed, so I gave a small donation for my visit.