On eof my greatest pleasures in life is walking beside either rivers or canals. The canal system in Britain is so fascinating I would recommend it to any visitor to spend at least half a day just exploring a canalside somewhere.
Many people come to Oxford and never even know there is a canal there. I suppose it's understandable with so many other interesting things to do, but I always like to have a little walk and look at the boats.
Should you want to walk the entire length (some 77 miles) all the way to Coventry, the website given is a good start point. It's another thing on my "to do" list!
To escape the noise and traffic of Oxford, try walking the canal path. You can get to it form town at the Hythe Street Bridge, or from Jericho near St. Barnabas Church.