This route crosses Oxfordshire from west to east before climbing into the Chilterns.
Beginning at Northleach in the Cotswolds, it follows the Windrush Valley on narrow lanes through a succession of villages, and pretty Burford, to the bustling town of Witney. The lane from Great Barrington to Windrush is a particular delight.
After Witney the route is unsignposted for a while, but you can follow the utilitarian cycle path beside the A40, picking up NCN 5 at the northern edge of Oxford towards the town centre.
In Oxford, the route passes colleges and chapels, heading out of town on the frenetic Cowley Road. Moderately busy roads lead to Thame where the lovely Phoenix Trail railway path makes for Princes Risborough. Here, a near-vertical climb (you'll have to push) marks the beginning of the narrow Chiltern lanes towards Chesham.