The Teynham 10 is a walk of 5 miles and should take around 2-3 hours depending on find speed. Number 13 should be given the maximum level of stealth and is the meanest seeing as it's no 13!
This is the final puzzle in the series, and a bonus from finding #14.
Puzzle #13 was codeword crossword, which can be found here...
Puzzle #14 was about the Teynham Commemorative Pump, which can be found here...
At #14 you were near a commemorative pump. On that pump was a year. What is that year? = ABCD (be careful)
In #13 you have values for letters P,U,M,P add the four numbers together to get? = EF
The cache can be found at...
N 51 (A+F) (A+B) . (D-A) (B+F) (D-E)
E 000 (B/2) (D) . (C) (B/2+A) (A+A+A)
If you want to double check the answer...

Congrats to SAS&A1 on the FTF of the entire series, and special thanks to them also for all their help in the snagging of these puzzles.