Planning a trip to Germany for December and trying to maximize the number of (good) Christmas markets we might see. Initially thinking about staying several days in the Koln area and using the DB to see several of the markets in the west (as well as Luxembourg). Wondering what city to use as a second base. Berlin? Hamburg?

We've done the markets in the south and are mainly interested in the northern portion of Germany. We have been to Trier, Mainz, and Frankfurt, but all were in the summer. Have never been to any of the northern cities at all.

Any suggestions for base cities that will maximize our ability to find markets? Or recommendations for markets not to be missed? Thanks!