The Völklinger Hütte is the single best reason to visit the Saarland region. This enormous 19th-century ironworks 10 km downstream from Saarbrücken was listed as a UNESCO World Heritage Site in 1994 — the first industrial monument to receive the designation. The blast furnaces, pipes, and cooling towers stand intact and rusted, and the scale is extraordinary. Allow at least half a day.
Metz, 70 km south in France, is an easy and rewarding day trip. The city has one of the finest Gothic cathedrals in France (the Cathédrale Saint-Étienne, whose stained glass windows span seven centuries) and the Centre Pompidou-Metz, a contemporary art museum in a striking Shigeru Ban building that rivals the Paris original in quality of programming. Luxembourg City, about 90 km west, offers a compact medieval quarter above dramatic river gorges and an excellent fine arts museum.