This cache is not at the published coordinates but is along the route of the Upton Pyne Circular Walk trail. You will not need to leave the footpath to retrieve this one.
You can get the information you require by visiting caches 12 to 25 and reading the top of the logs. Each cache has a word written on the top of the log, put these together in order to work out the location of the bonus.
The bonus cache is much bigger than the others in this series and has room for GCs and TBs. Please rehide as you found it to avoid it being discovered.