I really enjoy riding the Lahn cycle path between Weilburg and Lahnstein.
In places the path is very narrow. With the new handlebars of the MTBs. you have to stop and let oncoming traffic or overtaking people pass.
This lahn section is a popular canoe area, with many rental options on site. The flat Lahnradweg is recommended for a relaxed bike ride, for example. between the historic and interesting old towns of Limburg and Weilburg.