This is an x-rated event from Churchend (Gt Dunmow) in Essex to Goole (near Hull) in East Yorkshire. Most of the ride involves the Fens, so there's not a lot of elevation gain in total; the wind will potentially be the biggest challenge. You can see my route and route card on cycling.routes.fun, and track my progress using the dot-watcher mentioned there.
The event is organised by Thomas Deakins. More info on the Audax.uk website.