The Mountain Eagle is hiding the cache in its nest! You need to use your own eagle-eyes to gather some numbers to find this location.
The beginning of the trail begins at the listed coordinates. Parking is available nearby.
You will then need to proceed to the 'Telegraph pole' waypoint to gather some information, followed by the 'Viewpoint' waypoint.
Here you will find three rows of yellow numbers on the pole.
A = the 3rd digit in the middle, four-digit number
D = the two digits in the bottom number added together.
Viewpoint (get the binoculars out!):
I recommend taking a seat on this rock, you'll get dizzy standing up! All clues assume you are directly facing across the valley to the opposite hill.
B = the number of pine trees directly to your left at your elevation (approx. 100m away)
C = look at the valley towards your left and you will see a new-looking housing estate. Count the number of fields between this and the small car park towards your right in the valley (where the consecutive fields stop, it will be a single-digit number). Beware that field with a couple of trees in the middle of it is to be counted as one field and you are only counting those fields on the opposite side of the road from you. This value will be the same as B+D.
E = C minus (the number of windows in the prominent grey ruin on the opposite side of the valley plus the number of windows on the red house in the valley directly below you)
F = C minus A
The values of A - F should equal 21.
The cache can be found at N51 45.ABC W003 48.DEF
Please be aware that the high terrain rating relates to the steepness of the ascent to the viewpoint and the final cache location. No equipment is needed but some hardy gloves are recommended - you'll be scrambling on all-fours up steep, rough ground for ten minutes and coming back down on your bum!
As always, park with consideration, take a friend, take some nice (spoiler-free!) photos and know when to stop if your safety could be compromised.