Wurzburg, Germany is a stop along the Romantic Road (Romantische Strasse) and by far my favorite of the cities. I would recommend it as a day trip or even for a night. It's a university town situated along the picturesque River Main with a beautiful castle/residence on a hill to gaze at - day and night. We stopped at the gorgeous town on our way to Munich for Oktoberfest and what a choice!
The town itself has many beautiful churches (free for viewing, like most in Germany - you take this for granted when you go to another country, such as Spain). The Residence, situated on the other side of the River Main is just gorgeous from the outside (we did not have enough time to go in). Picture it - on a hill, over a river, vineyards below - simply perfection! The town itself is known for it's wine in funny-shaped bottles. History claims the monks shaped the bottles in such a way that they could fit it under the cloaks and sneak it anywhere/everywhere! There are also many cute walking areas and a daily market, which at the time we were there offered fresh pfefferlingen and stein pilz (local mushrooms that are delicious) - my favorite!
Other cities along the Romantic Road include Rothenburg ob der Tauber (a VERY cute, must-see, Christmas town, but would not recommend more than an afternoon here), Augusburg (near the end of the Romantic Road - cute, but nothing too special), Dinkelsbuhl, and Nordlingen, neither of which I have visited... yet.
the Residence on the River Main
most famous statue on the bridge - the Madonna