Agree, with Sharky, Isle Of Grain is worth exploring. There's a great cafe near Cliffe called Blue Planet.
If you don't want to climb over the north downs then get a train to Tonbridge. The whole of the Kent weald will then be your oyster which is pretty flat. You can do 50 or 100 miles easy on the flat through towns and villages such as Marden, Headcorn, Smarden, Pluckley etc down to Ashford where you could either ride back or get a train.
Alternatively you can stay north, from Rochester, through Gillingham, Twydall to Upchurch, through Sittingbourne to Faversham then along the Graveney marshes to Whitstable, you can then push on along the Viking Trail along the coast to Herne Bay and Reculver or from Whitstable take the Crab & Winkle Way to Canterbury. Another nice destination from Tonbridge is a rolling ride to Camber, Rye or Dymchurch. Fabulous riding and roads.
Happy to work out some routes for you or even meet up for a ride, long or short. Though as I'm in training for L-E-L at the moment won't be able to meet up until end of August.