In the morning, I rented a city bike for 12 euros from Radstation bike rentals under the Duetzer Bridge at Map Location: 50.936241, 6.962983 . I followed the river on the Cologne side to Bonn which is also on the same side.
The paved path is right along the river most of the way but there are two places where it leaves the river to go around some industrial sites. The first site is near Immendors and requires a big detour. There are signs all along the way. The second detour is just a few blocks near Auerberg. The detours include a few short stretches of street riding with cars.
The ride was about 22 miles / 35 kms each way and took about three hours each way at an easy pace with a lot of photo stops. I also had to stop a few times due to heavy rain and sleet.
The path is very scenic along the river with views of cargo boats, ferries, bridges, small villages, nice parks, heavily wooded areas, and farm pastures.