Rüdesheim sits at the southern end of the UNESCO-listed Rhine Gorge. The Middle Rhine between here and Koblenz is one of the most castle-dense stretches of river in the world, and a day on a Rhine cruise boat lets you see a dozen of them. Several Rhine passenger ferries and excursion boats operate from Rüdesheim and Bingen throughout the summer.
The Rheinsteig long-distance trail runs along the right bank of the Rhine from Bonn to Wiesbaden, and the section north of Rüdesheim through the gorge is excellent walking. A popular approach is to hike north from Rüdesheim toward Assmannshausen or beyond, then return by train. The path passes through forested ridges above the river with views of Ehrenfels Castle ruin below.
Bingen am Rhein, directly across the river by ferry, has its own medieval fortifications and the Mouse Tower on an island in the Rhine — legend has it that the wicked Archbishop Hatto was eaten alive by mice in the tower, though the building probably served more prosaic purposes as a toll and signal station.