This trip is still in progress.
Rothenburg was a small, pretty town with a nice wall and Christmas markets, and was a good place to spend Christmas.
Frankfurt was big, cold, and with a decent number of museums and galleries. Mainz had a pair of Gutenberg Bibles.
Malta was small but the weather was nice, it was easy to communicate, and there was history everywhere - whether that be some of the oldest prehistoric structures known to man, Medieval fortifications, or second world war era bunkers.
Tunis, built on the site of ancient Carthage, was only a few dozen miles from Malta, and so I planned to spend a weekend there. However, the only airline that flies between the two is TunisAir Express, which rates a solid 9/10 on the "airline sketchiness" scale. It's the feeder airline for TunisAir, which is rated as one of the worst airlines in the world, which should be a major warning sign. I still booked the flight, but things have gone wrong even before my first flight was due to take off - my return flight has been totally cancelled and I was rebooked a day earlier. That's not enough time to spend in Tunis, so I spend 2x more for a 7x longer itinerary to fly back to Malta via Paris instead! We'll see how it goes.