You are looking for a small (250 ml) plastic cliplock box which contains a logbook, pencil and sharpener, with a little room for a small trackables. For this cache, the clues are a little more cryptic. If you've looked at GC55F9Z "It's a gas!", you'll should get the theme. ;)
A = An Olympic first.
B = A rusty age in history.
C = ... and old lace?
D = Jean Michel Jarre's breather.
E = Superman's weakness.
F = Good for teeth and bones.
G = Bad for the Hindenburg.
H = A heavenly body close to the sun.
J = You could put a dog on this. ;)
K = Hi-tech chips in this valley.
L = Last one, and you'll need this to get the balloons up at the party!
Now for the formula:
N 51 degrees, K . (B * F + G - A - C) minutes;
W 000 degrees, (E + G) . ((J - D) * L + A + H) minutes.
(Note that this puzzle was re-worked on 3 October 2016, but gives the same coordinates as the old version, so no need to recalculate if you've already solved it.)
All approaches to GZ may get muddy at times, and as the woodland floor does not get much direct sunlight, and rainwater may hang around. Suitable footwear is therefore strongly advised and I don't think any approach is suitable for buggies, certainly if it is muddy. There are nettles at GZ, but at the time of placement, there was no need to actually go wading into them.
There are a few other caches also in this lovely woodland, and the Hog's Back series is nearby if you're feeling up to a longer walk.
A quick note on the recommended parking: Although it may seem a little distance away, this is because parking on the Research Park is not allowed, and vehicles left there may get removed. Alternative pay and display parking is available at the nearby hospital, but you should avoid visiting times! Off-peak visitors may well find some parking spots on residential roads, but do check the restrictions. The supplied trailhead coordinate shows one way into the woods from the suggested parking direction.
Congratulations to ===sgb for the FTF.