Central Koblenz is small and walkable — the Altstadt fits inside a roughly triangular kilometre between the two rivers, and the main station is fifteen minutes' walk from the Deutsches Eck. The cable car is the practical way across to Ehrenbreitstein.
Local buses are useful only for outlying destinations like Schloss Stolzenfels (bus 650). Bicycles are available from a network of hire stations; the Rhine and Moselle riverside paths are flat, well-marked and good for half-day rides.