Set for the 2018 Winter Geolympix with permission from the National Trust. If you intend to attempt the Letter/Box Challenge on Mega day you may want to leave this until then.
Start at Post 1 at N51° 48.508' W0° 35.512' (Given co-ords)
You're looking for a green plaque on it.
If there's a D on it, use N -0.482 W -0.176 to calculate fresh co-ords.
If there's a H on it, use N +0.079 W -0.152 to calculate fresh co-ords.
If there's a L on it, use N +0.151 W +0.088 to calculate fresh co-ords.
And so on!
Post 2:
A N -0.088 W -0.219
C N +0.222 W -0.065
E N +0.004 W +0.026
Post 3:
C N +0.136 W +0.103
A N -0.381 W +0.186
N N +0.234 W -0.410
Post 4:
K N -0.098 W +0.077
E N +0.104 W -0.173
Y N +0.078 W -0.110
Post 5:
W N -0.026 W -0.166
H N +0.006 W -0.244
O N +0.111 W -0.322
Post 6:
C N +0.079 W -0.029
B N +0.104 W -0.319
A N -0.048 W +0.014
Post 7:
C N -0.050 W -0.104
S N -0.030 W +0.004
I N +0.110 W +0.044
Post 8:
H N -0.092 W +0.033
A N +0.131 W -0.109
T N -0.071 W -0.097
Post 9:
L N -0.129 W -0.115
A N +0.034 W +0.082
B N -0.051 W +0.044
Post 10:
S N +0.140 W +0.005
E N -0.068 W -0.101
T N -0.015 W +0.049
This should deliver you to the final!
Good luck. Please DO NOT remove the stamp or ink pad. Neither is a swap - They make this cache a LetterBox/Hybrid. Thank you!