Hanging Stones
The cache, a camo-taped 35mm film pot, is hidden on a wooded hillock on the northern edge of, and overlooking, a large abandoned quarry.
To reach the cache location: park at the Cow & Calf parking area off Hangingstone Road @ N 53 55.002 W 1 48.034 and head for the huge Calf rock below the Cow cliffs. From here, you can either scramble up through the tumble of boulders to the upper level or walk on past the Calf and, using any convenient trail, make your way upwards to the cache location.
What's in a name? The evocative name of this location is nothing to do with hanging. The rocks were first described as the Hanging Stones in the local parish records of 1645, and their name probably derives from the old-english word hangra, meaning ‘a wood on a steep hill-side,’ which is very apt here.
'Hanging Stones' appears three times on the 1851 Ordnance Survey map. It is a) the name of the first quarry indicated (incorrectly?) as where the Cow & Calf Hotel now is, it is b) the name used for the rocky outcrop to the east of the 'Ilkley Quarry' adjacent to the Cow & Calf - the famous large rock formation consisting of an outcrop and boulder (aka Hangingstone Rocks) - it is c) the name given to the wooded rocky ridge running west of the Cow & Calf rocks towards Backstone Beck and it is d) the name given to a residential area (HS Houses) in Ben Rhydding north of the the ridge.
Moving forwards to 1895 a) and b) have disappeared and the term is used for c), d) without the 'Houses' and now e) in large letters as Hanging Stones Quarries for the large area south of the cache location. Ilkley expanded rapidly from the 1850s for the next 40 years with the booming hydrotherapy trade and the large quarry (together with smaller ones shown to the south, not on the 1851 map) would have been used to extract the gritstone for building purposes.
By 1901, the term is still used for c) [although extended to cover all the rocky outcrop including b) above], d) and e), and three smaller quarries are shown as 'Old Quarries' maybe reflecting the end of the building boom with reduced need for stone.
Interestingly, the 2020 OS map does not use the term for any of the above - but only for the stretch of the adjacent road (which leaves Ilkley as Cowpasture Road) from its Backstone Beck crossing (near the cattle grid) as far as the hotel, where it becomes Moor Road. None of the other quarries are shown.
Neolithic Art: Some 70m west of GZ @ N 53 55.011 W 1 48.378 is the location of Hanging Stone Rock, one of the most notable and best known neolithic carved rocks (of which there are many) on Rombald's Moor.
This prominent outcrop bears several carvings on its flat upper surface the best preserved being found on the western panel. Some of this may have been covered in heather for a prolonged period keeping the carvings as sharp as they appear today.
The carvings on the eastern panel, however are very worn and hard to see clearly unless the lighting conditions are right. What appears to be two carved bowls on the southern edge of the outcrop strongly differ in appearance from the many natural weathered bowls on the moor and seem likely to have been carved or emphasised.
What is recognised as one of the finest examples of rock art in the UK was very nearly lost to quarrying during Victorian times. A Hydrotherapist from Ben Rhydding (Hydrotherapy Establishment) noticed the carvings and appealed to Squire Middleton to halt the quarrying at the location just in time. The Rock is a Scheduled Monument - see here for the Historic England listing.
At the northern foot of the outcrop is a recess/shelter known as the 'Fairies Parlour' or the 'Fairies Kirk' (as shown on the 1851 OS Map).
Reputedly, the Saxons tried to build a church nearby, only to find each morning that the building stones had been moved away further down the hill. After a few days of this, they gave up and built the church down in the valley. This may be a distant memory of the site's old ritual purpose.
See also: here for an interesting, interactive 3D model of the Rock, here for a comprehensive detailed description, photographs, plans of the stones and their motifs, photogrammetry and 3D models, here for a fascinating blog page on the Stones and the Fairies Kirk and here for another page with detailed description, photos and drawing.
Little Beauty: 
Finally, the large quarry near GZ - especially the area adjacent to the steep rocky southern and western edges - is the home of a colony of stonechats (Saxicola rubicola).
Its English name derives from its call, sounding like two stones being knocked together (listen in the videos - links below). The scientific name Saxicola means 'rock-dweller' from the Latin saxum (rock) + incola (dwelling in) and rubicola (bramble-dweller).
Although originally thought to be in the thrush family (to which chats are convergent), it is now considered a species of the Old World flycatcher family.
They breed in heathland, coastal dunes and rough grassland with scattered small shrubs and bramble, open gorse, tussocks or heather where they are frequently seen flicking their wings while perched, often on the tops of low (preferably gorse) bushes.
They are short-distance migrants or non-migratory, with part 
of the population (especially from the NE parts of the range, where winters are colder) moving south to winter further south in Europe and more widely in North Africa.
They are mainly insectivorous, feeding on caterpillars, moths, ants, spiders and flies, though they will also take worms and snails, and feed on seeds and berries in the autumn and winter. They have an average lifespan of 4-5 years.
During hard winters their numbers may decline drastically, but like many small birds, survivors are thereafter able to reproduce very rapidly having up to 4 broods a year, each with 5-6 young. This means that populations can bounce back much quicker than other species which have only 1-2 broods.
See here for details of this lovely robin-sized bird, and watch short videos here and here.