Rheinpark gives Cologne room to breathe. Spread along the right bank of the Rhine in Deutz, it trades the tight streets around the cathedral for lawns, paths, river air, and one of the best skyline views back toward the old town.
It is especially good at the end of a busy sightseeing day. Cross by the Hohenzollern Bridge, wander the river paths, and stay until the cathedral and bridges begin to light up across the water.