This cache series is not designed to be easy. The caches themselves are all quite easy to find, but determining the coordinates of each will require some puzzle-solving effort.
When you visit the cache, be sure to take a printed copy of the bonus puzzle sheet [PDF] so that you can decipher the coordinates of the secret bonus cache! Alert: You are about to download a file that contains further details needed to find the secret bonus geocache. As the cache owner, I represent that this file is safe to download although it has not been checked by Groundspeak or by the reviewer for possible malicious content. Download this file at your own risk.
The image below looks like gibberish, but if you look at it the right way then you'll see that it clearly contains the coordinates of the cache.
Can't see it? The image itself is very special, and it might be that it's impossible for you to decode while you're just looking at it on this web page. Perhaps there's something else you need to do to be able to see it. For more tips, see the supporting web page for the cache series.
Note that parking is restricted to residents only. There are a small number of public parking spaces on Whitehouse Road (at the waypoint coordinates given) but these often fill during the daytime. Consider walking or cycling from the City Centre or taking the bus into Oxford if you're travelling from elsewhere.
Need a hint to help decipher the coordinates? You might find what you're looking for on the supporting web page.