Follows the Wandle, a small river in inner South West London, though surburbia and several small interconnecting local parks. It starts in Wandsworth on the banks of the Thames (itself a popular cycle path), and heads south towards Wallington.
Highlights are Morden Park NT and Merton Abbey Mills. The path will be busy with school kids during rush hour and families and at weekends.
It can be extended towards East Croydon, but although cycle friendly, this part has quiet on-road sections.
Note that between the Thames / Wandsworth Park and the start of the walk is Wandsworth's short but scary 1-way system. Best to walk if nervous or with kids.
It quite difficult to follow the route from an OS map, or signposts alone - it is well waymarked, but best to download the map from either the Merton Council website.
The river has an industrial history. Its quite fast flowing, so was used for water power. There were also cress beds (now a nature reserve) near Morden Hall (NT)