A multi stage clamber on Dartford Heath.
At the co-ordinates you will see a yellow sign.
Number of words on the 3rd line A and letters in the last word on the 4th line, B.
Now head to N51 26. A+B A+B+A A-A E0 11. A B-A B+A
You will see a post here with a letter on it, C (if M=13) and the word Dartford on it D times.
Now head to N51 26. C-D D-2A B-A E0 11. C/B D+A D-A which will take you via GC7GENE.
On the way there (update 19/8/24: the original cover has been replaced but instructions improved to find another one) you will come across a silver cover 15m off the left of the path, just after a medium sized tree, with a yellow symbol on it. Number of sides of the symbol, E. There are two letters on it F and G. Further update 8/3/26: all of them now seem to have gone so now look for their tall black replacements and the name of the company that fabricated them (white writing on blue background). E=1st letter, F=5th letter, G=1st+3rd+4th letters. If you get to the trad then you've missed it.
And you go past H posts like the first one (don't count where you start or finish)
The cache can be found at N51 26. F-A F-H G/E E0 11. B-H G/D C-B
This cache is 7-8m up a tree. It should be fairly easy to free climb.