The cache is not at the published coordinates
They are for Headington car park which is about 12 minutes walk from the cache location - a peasant walk through part of Old Headington.
Parking in Headington is mostly for residents only. There are a few free 2 hour slots - you might be lucky enough to find one but I recommend using the car park, it costs £1.60 for 2 hours parking , enough time to do a few of the local caches. Do not try to park in the small road leading to the cache as this is private parking only.
To find the cache you must solve the following puzzle.
N51(Flora+Leda).(Fortuna-Fortuna)(Doris+Flora)
W001(Hebe+Hebe).(Iris)(Circe+Ceres)