GEOCACHING ON NATIONAL TRUST PROPERTY IS AT YOUR OWN RISK.
Also, please note that the National Trust is caring for the specialist habitats and landscape you enjoy on this and other caches on NT property, which is one of the reasons we are glad to be members.
Stage 13 (at last!) - a cache page puzzle
Well done on making it this far! Time to reflect on what you have achieved so far for the Westing, and use your head very figuratively (unless really lazy) for the Northing.
N51 and W000 as usual
Northing: 41.37(5-2)
Westing: (VG+NX).(NX+MY) RR (NG+NM)
Here is a link to the hints pages, which will help you to solve the puzzle, and which you can click on if you get stuck.