The Abbey waypoint is N 50° 48.788' E 004° 26.708' .
If you choose to go there from the abbey, follow the path on the left side of the lake and then stay on the left side of the creek. At a certain point you'll have to leave the path to climb the hill for about 100 m.
Look under an old stump. It is covered by pieces of logs to hide it.
2nd September 2013 : There is a large wasps nest in the ground about 2 minutes away from the cache site. If you walk up the gulley from the lower footpath, it is slightly the the left at the top. Thanks to theoriginaldunk for the "warning message"