The description for this series of caches can be found on the first cache's description at https://coord.info/GC7FQYA and the assumption is made that you are doing these caches in order
From cache four you should head west through the wood. It might seem a long way… At the given co ordinates you will see a yellow sign. -something- Valley Walk. Count the number of letters in that -something-, and let that number be A
-THE CACHE IS NOT HERE- it is at N51 09 A-1 A+1 A-A E00 48 A+1 A-2 A-1. Follow the path keeping the woods to your right until the path goes into the wood. You should see your target from there