In addition to the long-established Christmas market in downtown Frankfurt as well as the popular Christmas markets in major cities such as Aschaffenburg, Hanau, Offenbach, Darmstadt, Wiesbaden or Mainz, there are also numerous smaller but often all the more atmospheric gems to be found in the districts of Frankfurt as well as throughout the Rhein Main area, such as
The "Christmas Market of Nations" in the romantic Old Town and the world-famous Drosselgasse in Rüdesheim
the "Bergweihnacht" on the Johannisberg in Bad Nauheim
the "Odenwald Christmas Market" in the romantic half-timbered town of Michelstadt
the "Romantic Christmas Market" at the Landgrafenschloß in Bad Homburg
the "Historical Christmas Market" at Ronneburg Castle with the unique ambience of the Middle Ages
These are admittedly only a few examples.
You can find an extensive selection of Advent, St. Nicholas and Christmas markets in the Frankfurt RhineMain region at: https://www.frankfurt-tipp.de/veranstaltungen/eventcat/weihnachtsmaerkte.html
More Christmas Specials:
The Frankfurt Christmas Market
The Christmas Tree and Other Symbols
Christmas traditions around the world - part 1
Christmas traditions around the world - part 2