Most Geocache locations are found by knowing or working out the
latitude and longitude but the third 'tude' rarely gets a look-in:
either because the setter's smartphone didn't show it;
or because these pages don't have a place for it;
or out of sheer deviousness.
(You know who you are ...)
This is where altitude comes into its own.
Longitude: W 003 50.046
Altitude: 444 m
IMPORTANT! Check your GPS shows the true altitude by visiting an OS map spot height. (The Waypoints given below also declare correct altitudes.) If a correction is necessary, memorise it.
See below for the explanation.
Getting to GZ:
The cache is not at the published coordinates (surprise!)
Altitude 444 m: weather-proofs and sturdy boots.
Sheep country: Keep your dog under close control.
Slow and steady: GPS receivers need time to calculate altitude.
On the right route you WON'T have to negotiate any crags or tricky burns, nor climb over any walls.
Even then, it's not too accurate: Cachers' nose is needed here.
Under a stone by a drystane dyke: This cache is off the wall, not in it.
More about altitude
A GPS doesn't calculate its altitude directly, like latitude & longitude: It works out its distance (call it r) from the centre of the Earth and also the distance from the centre of the Earth to what sea level would be at that latitude and longitude, then subtracts that from the value of r and shows the result as the altitude.
The Earth is not a perfect sphere, but is slightly squashed (an idealized ellipsoid calculated for a spinning globe). Then the GPS corrects that for deviations caused by mountains, deep ocean trenches and differences in the density of the rocks using a detailed mathematical model of the shape of the Earth: the Geoid.
Here's link to an image of the Geoid, exaggerated to illustrate the shape clearly: Image of geoid, from ESA.
Europe lies in a region roughly 60 metres further from the centre of the Earth than the idealized reference ellipsoid. So if your device doesn't do the Geoid correction, it thinks sea level around here is 60 metres lower than it should be and so gives an altitude reading 60 metres too high. Some so-called Smartphones show this effect so the moral for smartphone users is: Go to a spot height on an OS map, get your device to show the altitude, memorise the correction!
Surveying by levelling (as on OS maps) gives true altitudes relative to sea level. Your CO originally set up the cache using a Garmin Etrex H and has found that the altitude it shows (after settling) is close enough to that on OS maps for the purposes of the bit of nonsense we call Geocaching ...