Route: Outer Aylesbury Ring (UK)

85km, 1,218m ascent, circular off road route on footpaths around the town of Aylesbury, touching the northern edge of the Chilterns. The route is marked by signposts with a special logo. 

https://www.ldwa.org.uk/ldp/members/show_path.php?path_name=Outer+Aylesbury+Ring has more details. 

Note that this is the longest of 3 Aylesbury "ring" routes:

https://fastestknowntime.com/route/aylesbury-ring-united-kingdom, 51km

https://fastestknowntime.com/route/round-aylesbury-walk-united-kingdom, 20km