Děčín sits where the Elbe cuts between sandstone cliffs on the Czech-German border. It is not as polished as Prague or as famous as Český Krumlov, but the setting is excellent: a castle above the river, a rock wall with a via ferrata in the middle of town, and forested hills leading into Bohemian Switzerland.
Start with Děčín Castle, which rises above the confluence of the Elbe and Ploučnice rivers. Across the water, Pastýřská stěna gives the city its best adventure: protected climbing routes with castle and canyon views. If you want something slower, follow the river north by boat or on foot toward the sandstone country that begins almost at the edge of town.
Děčín works well as a one-day stop between Prague and Dresden, especially if you like your small cities with a little grit. It is also a practical base for the western side of Bohemian Switzerland, though the town itself has enough to justify the stop.