Donauwörth's position at the junction of the A7 and the Romantic Road makes it a convenient base for a cluster of destinations that are individually worth a detour.
Harburg (10 km north) — Harburg Castle rises on a rocky spur above the Wörnitz valley and is one of the best-preserved medieval castles in Germany. Unlike many German castle ruins, Harburg was never significantly destroyed and has been continuously inhabited: it remains in the hands of the Oettingen-Wallerstein princely family, who have owned it since the 18th century. The interior rooms — including the treasury, the torture chamber, and the great hall — can be visited on guided tours. The village below the castle has a couple of quiet places to eat.
Nördlingen (45 km north, about 45 minutes by regional train) — Nördlingen is one of only three towns in Germany where the complete medieval wall circuit survives intact and can be walked in its entirety. The wall encloses a nearly perfect circle, because the town was built inside a meteor crater — the Nördlinger Ries, created around 15 million years ago — and the impact geology gave a naturally circular depression to build in. From the tower of St. George's church you can see the crater rim forming the horizon in every direction. The town itself is quieter and less polished than Rothenburg, which is part of its appeal.
Augsburg (30 minutes by train) — Augsburg is a proper city with a serious Roman and Renaissance heritage. The Fuggerei, the world's oldest surviving social housing complex (built 1516, still inhabited, rent still set at one Rhine guilder per year in nominal terms), is the most unusual sight. The town hall and the Maximilianstraße are the grand set pieces. Half a day is enough for a focused visit; a full day covers most things.