A ride of thirds - North-West London, the Chilterns and the flatlands to Oxford. Along the way there are many delights, Northala Park with their three big cones, Chesham and then the delights of Great Missenden and the Chiltern Lanes. Fly down the scarp slop to Princes Risborough and onto the perfectly flat and well-surfaced ex-train line to Thame. There's one of the nation's great gardens to distract you before the surprisingly industrial entrance to the city of academia.
Be aware, that as with all my routes, this is a mixed surface route and includes short sections of woodland trails. There is nothing a 28mm road tyre cannot cope with. As a day out from the capital, this is a good one.