My suggestion for a longer loop.
Frrom Watlington town car park, up Hill Road, left onto Swans Way to Dame Alice Farm, then up to Woods Farm then Cookley Green. Bridleway past nature reserve to Bix Bottom. Oxfordshire Way, then Warmscombe Lane to Middle Assendon. Road to Fawley Bottom then Fawley, then Bridleway from Roundhouse Farm to Reservoir Hill, the on to Upper Woodend Farm. Road to Kimble Farm, then offroad to Turville, then Turville Court, Turville Heath. Holloway Lane to Northend, bridleway from Launders Farm, Oxfordshire Way towards Stonor. Road into Pishill. Offroad to Russels Water.
At this point anyone that’s had enough can retrace the outward route through Cookley Green and Woods farm to Watlington.
For a longer route bridleway from Russels Water to Westwood Manor Farm, turn right to Park Corner. Follow the Chiltern Way past Harcourt Hill then right onto Swans Way. Then right onto Ladies Walk, Colliers Bottom, then onto road – Church Lane- back to Cookley Green, then back to Woods farm for a nice descent to Dame Alice Farm, then a bit of the Swans Way before you head down the hill to the car park and the pub.