One of my favorite cities in Germany is Freiburg. Nestled at the foot of the Black Forest (and just north of Basel, Switzerland), there is a plethora of things to do and see here.
There is a Museum of Early and Pre-history, located in the Columbi Palace (built in 1861). There is a Carnival Museum, a Historic Merchant's Hall, and a gorgeous cathedral. A Modern Art museum is wonderful to visit. There are gardens aplenty, and of course cultural activities and excellent food.
There is a road that goes right through a building - the Schwabentor, a gate within a building! I had never seen anything like it.
My favorite part of Freiburg is the Munsterplatz, in which the cathedral is located. We stayed at a quaint hotel right on the Munsterplatz (with fantastic breakfasts!) and enjoyed the morning market more than once. It is glorious, to wake up to the sounds of the market, and then wander down and stroll through it.
Don't pass through southern Germany without visiting this vital, historic town! Of all the cities I visited in Europe, I ate the best in Freiburg. I sat in on outdoor music concerts, visited the market, ate lovely food, drank coffee and beer - and everyone was so friendly and kind.