Rickmansworth, the Chilterns and Chess Valley
metropolitan line, or by train from Marylebone, there is a 9.27 arrives 9.49.
This is one big cheat! I will be in France so I was looking for something well described and this fits the bill. We did it a couple of years ago in the other direction, in the winter with Margaret Hyde but I think it will be sufficiently different in June, backwards! It also continues where we left off in April, at Rickmansworth station.
I suggest you start at 10 am at Rickmansworth station which is accessible on the metropolitan line, or by train from Marylebone, there is a 9.27 arrives 9.49.
Here is the walk:
http://www.chilternsaonb.org/uploads/files/Walks_and_Rides/chess_valley_...
This link gives all the required detail, contact me if you have a problem downloading it.