This is an easy and attractive ride using the Sustrans cycle route 5 which includes the Thames Path and minor roads. As a historic city, Oxford has many attractions for the tourist whilst Abingdon is a pretty market town with abbey ruins, medeival houses, parks and leisure facilities.
Starting from Carfax in central Oxford, head down St Aldate's to Folly Bridge. Go over the river and then take a left down a ramp onto the Thames Path. You shortly go over a bridge. Continue along the Thames Path (look out for walkers and cyclists shouting at boat crews through megaphones) until you come to Iffley Lock. Stop and admire the flowers. Continue along the Thames Path until you come to a cattle grid. At this point the Thames Path goes off to the left and you continue along a hard surface beside the railway track. At the end of this you have to turn right up the hill. Now follow signs for Sustrans Route 5 through Radley. You eventually join a former railway track alongside some disused gravel pits, now lakes. This takes you into Abingdon where you can stop for a swim in the open air pool or have a cup of coffee and decide whether to continue to Didcot or return by the same route to Oxford. It's up to you.
Hanson Way - National Route 5
Oxford - Abingdon