Beginner route request

Hi all, wasn't sure if there's a more appropriate place to ask this!

My girlfriend's been cycling properly for the first time in years during the last few months, just nipping around London and the parks.

She's keen to ramp it up a bit, good fitness from regular running but no real cycling experience outside of functional needs, and we're both on single speeds. Does anyone have recommendations for roughly 20 mile, largely flat, rides that get us out of London and onto some quieter roads (ideally with some green scenery)? I'm east and she's west so can head out from any direction really, or happy to jump on the train and go from elsewhere if anyone has any good tips!

For reference, I did the 40 mile Dirty Wkend loop of Waltham Forest/Nazeing/Epping yesterday, but that would be way too much for her in terms of both distance and hills.

Thanks!

Check out RWGPS or Komoot or cycle travel. They give you a break down of the types of roads / tracks you want to ride. National cycle routes are pretty good - when route planning just change the map type to OSM cycle and it highlights all the cycle friendly routes.

Experiment and enjoy!

Thames path of some variety? Combined with Wimbledon common I think makes for a few miles off road on gravel and dirt.

Apart from routes, also investigate cycle training. It's started up again in various places and is great for beginners. Look for it on your/her local council web-site.

Thanks all for the resources, much appreciated!

Rides towards Windsor are generally the flattest as for the most part you follow the river, i've done a number of fixed rides that way. Would recommend bikemap.net & ridewithgps.com/ as you can search for locally built routes