Once you have solved the puzzle below, you will need to substitute the seconds in the answer that you calculate with those given here.
N dd:mm:26.1
W dd:mm:37.4
And so to the puzzle:
The numbers below, when paired correctly, should be used (in a way in which you need to determine) to give you three sets of co-ordinates. As there are seven numbers below you will also have spare:
0.048452693
0.052616761
0.055497183
0.750005258
0.782789206
0.783521777
0.784313417
The three sets of co-ordinates each give the location of the same type of common feature. These form a triangle, the point at the centre of mass of which has co-ordinates which give the degrees and minutes you need to combine with the seconds given in the introduction. To check that you have the right point for the centre of mass, the spare left from above (when suitably treated as with the other six) should relate to the difference between the easting (ignore any minus) and the northing of that point in the same way as the rest of the numbers relate to co-ordinates.
All points referred to are to be found on Landranger sheet 171.
Please make sure you put the cache back hanging from the top of the surrounding location so that it does not sit in any moisture that forms.