We first discovered this route when we decided after a winter of riding in Surrey to be a bit adventurous, so we signed up for an Audax ride over in Maidenhead. The cafe we meet in is fairly disgusting but the route is fantastic looping in and out of the Thames valley crossing about ten bridges as it works its way up to Windsor Great Park. 100 + Km, first third has a few climbs, then it settles to something very manageable.
N.B. For those of you who have difficulties with BikeRouteToaster if you scroll to the bottom of this posting you'll find you can download the TCX files from this page