Wandle Trail started in Wandsworth. There is a lot of major building work going on (RAM building) so got onto Garrett Lane
First mile is road but once you get into Geirges park you are on cycle track but you can hug park.
After that you hit Wandle trails for most of the route. The paths are varied from tarmac to grass and gravel. Some of the trails hug the river and most of the time you are surrounded by wonderful nature
For a London route you uncover many wonderful nature parks, sanxturies, farms etc Route goes through a National Trust.
Route is mostly straight forward where you can follow blue cycle signs. There are a couple of occasions where the cycle route goes one way and there is a walking route oprion that goes another - they invariably meet back up.
On my Strava you will see a couple of very minor mistakes where path isn't obvious. My Coros was accurate and easy to use to get back on course pretty quickly.
Highly recommended this route. Its flat so no advantage either direction. For those coming from central London I'd be tempted to opt for train to Croydon - short walk to Wandle Park where the start is by the Wandle St and run back into London